Monocrystal lead strontium titanate film and preparation and application thereof
The single-crystal strontium titanate film epitaxially grown on a single crystal strontium niobium doped single crystal substrate by low temperature hydrothermal method, solving the problem of growing high-quality films at low temperatures, and achieving the preparation of high-quality strontium titanate films at low temperatures, with good pyroelectric response and wide application prospects.
Patent Information
- Application Number
- CN202510786082.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-12
- Publication Date
- 2025-07-25
AI Technical Summary
It is difficult for the prior art to grow high-quality strontium lead titanate single crystal thin films at low temperatures, and conventional methods have problems such as complex equipment, high cost, and unstable film performance.
A single-crystalline strontium titanate film was epitaxially grown on a single crystal substrate of strontium titanate doped by low-temperature hydrothermal method. By adding tetra-n-butyl titanate, strontium carbonate and lead carbonate to an aqueous potassium hydroxide solution, and hydrothermal reaction was carried out to prepare a high-quality large-area film with a single <001> orientation, atomic level interface and micron thickness.
It has achieved the growth of high-quality single-crystalline strontium titanate films at low temperatures, with good pyroelectric response, and is suitable for security monitoring, human body detection, infrared imaging, intelligent temperature control and night vision equipment, and has a simple process and easy to produce on a large scale.
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Abstract
Description
Technical Field
[0001] The present invention relates to titanates, and particularly to single-crystal titanate thin films and their growth and applications. Background Art
[0002] The pyroelectric effect refers to the charge release phenomenon manifested by the change of polarization intensity with temperature. Macroscopically, the change in temperature causes a voltage to appear at both ends of the material or generates a current. Pyroelectricity is an inherent basic physical phenomenon of polar materials. For crystals with spontaneous polarization, when the crystal is heated or cooled, due to the change in temperature, the spontaneous polarization intensity changes, resulting in surface polarization charges being generated in a certain direction of the crystal. In recent years, this effect has attracted extensive attention in different fields, covering various fields such as infrared detection, temperature sensing, and thermal energy harvesting.
[0003] ABO3 perovskite-type ferroelectric materials are typical representatives of pyroelectric materials, with characteristics such as oxidation resistance, high temperature resistance, moisture resistance, radiation resistance, simple process, and low cost. Lead strontium titanate (Pb 1-x Sr x TiO3, abbreviated as PST) is a ferroelectric material with a perovskite structure, which is a solid solution of lead titanate and strontium titanate. In the PST structure, the Ti 4+ ion has a relatively small ionic radius (about 0.068 nm) and can perform anharmonic vibrations within a small range and deviate from its equilibrium position. In the ferroelectric phase, this deviation causes the Ti-O bond to displace along different crystal axes (such as the four-fold axis, two-fold axis, and three-fold axis), triggering lattice distortion and generating spontaneous polarization. Introducing Sr 2+ with an even smaller ionic radius (about 0.112 nm) to replace part of the larger-radius Pb 2+ (about 0.118 nm) occupying the A site will contract the lattice and increase the spatial mismatch between the A-site vacancy and the Ti 4+ ion. This enhanced spatial constraint forces the oxygen octahedron to undergo more significant distortion and prompts the Ti 4+ ion to undergo a larger displacement, thereby directly enhancing the spontaneous polarization intensity of the material. Therefore, this substitution helps to obtain an improved pyroelectric coefficient at room temperature, synergistically optimize the dielectric properties, and ultimately enhance the pyroelectric performance.
[0004] With the development of microelectronics technology and nanotechnology, the application potential of PST materials in the fields of integration, miniaturization, and low power consumption is also increasing continuously. However, most of the existing PST thin films are polycrystalline materials, facing challenges such as high defect density, high ion mobility, significant non-radiative carrier losses, and environmental instability. In particular, there are high concentrations of defects on the surface and within the grain boundaries of the thin films, which can trap photo-generated carriers, leading to a large amount of non-radiative recombination and thus severely damaging the device performance. In addition, the intrusion of oxygen and water molecules along the grain boundaries can cause the degradation of the thin films, thus posing a challenge to their long-term stability. Relatively speaking, single-crystal thin films have excellent crystal structures and fewer defects, which can provide more uniform electric field responses and higher pyroelectric properties, avoiding the negative impacts of grain boundaries and defects in polycrystalline materials on performance. Secondly, the pyroelectric properties of single-crystal thin films are more stable. Their high crystal symmetry and less internal stress enable them to respond more precisely when the temperature changes. In addition, single-crystal thin films are suitable for compatibility with microelectronic devices and integrated circuits, enabling the realization of high-sensitivity and low-power pyroelectric sensors and energy harvesters. Therefore, there is an urgent need for the preparation of PST single-crystal thin films in high-precision pyroelectric applications.
[0005] At present, the preparation methods of lead strontium titanate thin films, especially PST single-crystal thin films, still face many challenges. The commonly used pulsed laser deposition method (PLD) and liquid phase epitaxial growth method (LEP) have certain limitations.
[0006] Among them, although the PLD method can achieve the epitaxial growth of high-quality thin films, it usually requires high equipment costs and complex process control.
[0007] For example, XT Li, PY Du et al. published an article titled "Structure and dielectric properties of highly (100)-oriented PST thin films deposited on MgO substrates" in 2008 (Thin Solid Films, 2008, 516, 5296 - 5299). They used the PLD method to prepare lead strontium titanate thin films, but the formation of the crystalline phase and the orientation of the PST thin films are very sensitive to the deposition temperature. Only at relatively high deposition temperatures (such as 780 °C) can highly (100)-oriented polycrystalline thin films be obtained; at lower deposition temperatures, the orientation of the thin films is poor and the content of the crystalline phase is low, which limits the further improvement of the thin film performance.
[0008] For another example, Alexander N. Zherikhin pointed out in an article titled "Pulsed laser deposition of thin films" (Tenth International School on Quantum Electronics: Laser Physics and Applications, 1999, 3571: 72-79.) that the PLD method produces micron-sized droplets due to laser ablation of the target material, and it relies on a high-speed rotating mechanical filter to reduce contamination, resulting in complex equipment and difficulty in large-scale production. At the same time, its plasma diffusion efficiency is low, and it is impossible to achieve micron-thick films.
[0009] Similarly, the LED method also has significant technical bottlenecks. For example, Laura Wollesen et al. reported in an article titled "Tunable crystalline structure and electrical properties of (Pb,Sr)TiO3 films grown by liquid phase epitaxy" (CrystEngComm, 2023, 25, 2096–2103.) that when preparing lead strontium titanate single crystal thin films by the LEP method, they are grown in a high-temperature environment above 800 °C (far exceeding the Curie temperature of lead titanate, 490 °C), resulting in a phase change during the cooling process, triggering lattice distortion and a / c axis orientation mixing defects, making it difficult to control the structure and properties of the thin films. Summary of the Invention
[0010] In view of this, the purpose of the present invention is to provide a lead strontium titanate (Pb 1-x Sr x TiO3) thin film and its preparation and application. The lead strontium titanate single crystal thin film is a high-quality large-area single crystal lead strontium titanate thin film with a single <001> orientation, an atomically flat interface, and a thickness up to the micron level. Under the irradiation of infrared light with a wavelength of 1064 nm, it has a self-driven pyroelectric response. The preparation method of the present invention is a low-temperature hydrothermal method, which is simple and easy to operate, and the raw materials are simple and easy to obtain, solving the problem that it has been impossible to grow high-quality lead strontium titanate single crystal thin films at low temperatures for a long time.
[0011] To achieve the above purpose, the present invention adopts the following technical solutions:
[0012] The present invention provides a lead strontium titanate (Pb 1-x Sr xThe (Pb1-xNbx)TiO3 thin film is a thin film epitaxially grown on a single crystal substrate of strontium titanate doped with niobium. The thin film has a flat and continuous surface and an atomically flat interface, and the thickness of the thin film is 80 - 2200 nm.
[0013] In some specific examples of the present invention, 0 < x ≤ 0.15.
[0014] In some specific examples of the present invention, the thin film is a large-area thin film, and the area of the thin film is close to cm 2 level.
[0015] Meanwhile, the present invention also provides a method for preparing the above-mentioned single crystal lead strontium titanate thin film, including the following steps:
[0016] (1) Under stirring, tetrabutyl titanate is added to an aqueous potassium hydroxide solution, and after sufficient stirring, a mixed solution is obtained; then strontium carbonate and lead carbonate are successively added to the mixed solution, and after sufficient stirring, a precursor suspension is obtained, and the precursor suspension is placed in the inner liner of the reaction kettle;
[0017] (2) The single crystal substrate of strontium titanate doped with niobium is placed in the precursor suspension, and then the inner liner of the reaction kettle containing the precursor suspension is placed in the reaction kettle, sealed, and hydrothermally reacted at 200 - 220 °C for 12 - 24 h;
[0018] (3) After the reaction kettle is naturally cooled, the kettle is unloaded; the product of the hydrothermal reaction is taken out, washed and dried to obtain the target thin film product.
[0019] In some specific examples of the present invention, in step (1), the final volume of the precursor suspension is 50 - 80% of the volume of the inner liner of the reaction kettle.
[0020] In some specific examples of the present invention, in step (1), in the precursor suspension, the molar concentration of titanium element is 0.11 - 0.28 mol / L, preferably 0.14 - 0.22 mol / L.
[0021] In some specific examples of the present invention, in step (1), the feeding molar ratio of strontium carbonate to tetrabutyl titanate is x:1, where 0 < x ≤ 0.15.
[0022] In some specific examples of the present invention, in step (1), the feeding molar ratio of lead carbonate to tetrabutyl titanate is (1 - 1.5)×(1 - x):1, preferably (1.1 - 1.3)×(1 - x):1.
[0023] In some specific examples of the present invention, in step (1), in the precursor suspension, the molar concentration of potassium hydroxide is 3 - 6 mol / L.
[0024] In some specific examples of the present invention, in step (1), after adding tetrabutyl titanate, the stirring time is 2 to 30 minutes.
[0025] In some specific examples of the present invention, in step (1), after adding strontium carbonate and lead carbonate, the stirring time is 2 to 3 hours.
[0026] In some specific examples of the present invention, in step (2), in the niobium-doped strontium titanate single crystal substrate, the niobium doping concentration is 0.05 to 1.0 wt%, preferably 0.5 to 1.0 wt%, and most preferably 0.7 wt%.
[0027] In some specific examples of the present invention, in step (2), the orientation of the niobium-doped strontium titanate single crystal in the niobium-doped strontium titanate single crystal substrate is <100>.
[0028] In some specific examples of the present invention, in step (2), the size of the niobium-doped strontium titanate single crystal substrate is 10 mm × 5 mm × 0.5 mm.
[0029] In some specific examples of the present invention, in step (2), the niobium-doped strontium titanate single crystal substrate is washed successively with acetone, ethanol, and deionized water before use.
[0030] In some specific examples of the present invention, in step (2), when the niobium-doped strontium titanate single crystal substrate is placed in the precursor suspension, the washed niobium-doped strontium titanate single crystal substrate is first fixed on a polytetrafluoroethylene support, and then the two are put together into the precursor suspension contained in the inner liner of the reaction kettle.
[0031] In some specific examples of the present invention, in step (3), the washing is to repeatedly wash the product of the hydrothermal reaction successively with deionized water and absolute ethanol.
[0032] In some specific examples of the present invention, the reaction kettle is a reaction kettle sealed with a stainless steel kit and a polytetrafluoroethylene inner liner. Among them, the polytetrafluoroethylene inner liner has good high-temperature and high-pressure resistance, and the stainless steel sealed reaction kettle sleeve is outside the inner liner to ensure that the inner liner does not deform during the reaction, so as to maintain a high-pressure environment.
[0033] In the present invention, the purity of tetrabutyl titanate, lead carbonate, strontium carbonate, and potassium hydroxide is not less than chemically pure. By mass percentage, the purity of tetrabutyl titanate ≥ 98.0%, the purity of strontium carbonate ≥ 99.0%, the purity of lead carbonate ≥ 99.0%, and potassium hydroxide ≥ 85.0%.
[0034] In the present invention, room temperature can be 0 to 40 °C, preferably 20 to 25 °C.
[0035] In addition, the present invention also provides an application of the above-mentioned single-crystal lead strontium titanate thin film. The single-crystal lead strontium titanate thin film responds to 1064 nm infrared light irradiation and can operate at zero bias voltage. Therefore, the single-crystal lead strontium titanate thin film has broad potential application prospects in the fields of security monitoring, human detection, infrared imaging, intelligent temperature control, night vision equipment, and medical diagnosis, etc.
[0036] Compared with the prior art, the present invention has the following beneficial technical effects:
[0037] (1) The high-quality single-crystal lead strontium titanate (Pb 1-x Sr x TiO3) thin film of the present invention is epitaxially grown on a niobium-doped strontium titanate single-crystal substrate. It has an atomically flat interface and a flat and continuous thin film surface. The thin film area is close to the cm 2 level (for example, 8 mm × 5 mm), and the thin film thickness can reach the micron level, which provides an effective way to obtain a thick single-crystal PST thin film. In contrast, techniques such as pulsed laser deposition (PLD) that are commonly used to grow thinner nanometer thin films face challenges in terms of efficiency or uniformity when depositing micron-level uniform PST thick films. The present invention solves the problem of difficult growth of micron-level, large-area single-crystal PST thin films. The high-quality single-crystal lead strontium titanate thin film of the present invention responds to 1064 nm infrared light irradiation and can operate at zero bias voltage, and has broad potential application prospects in the fields of security monitoring, human detection, infrared imaging, intelligent temperature control, night vision equipment, and medical diagnosis, etc.
[0038] (2) The preparation method of the present invention has a simple technological process, is easy to control, has a low cost, and is easy to scale up production. Moreover, the whole preparation process is below the Curie temperature, and the phase transformation between the paraelectric phase and the ferroelectric phase does not occur in the PST thin film structure during the preparation process. Description of the Drawings
[0039] Figure 1 is the X-ray diffraction (XRD) pattern comparison of the thin film products obtained in Examples 1 to 4.
[0040] Figure 2 is the high-resolution X-ray diffraction φ scan pattern of the thin film product obtained in Example 1.
[0041] Figure 3 is the X-ray diffraction rocking curve pattern of the thin film product obtained in Example 1.
[0042] Figure 4 is the scanning electron microscope (SEM) picture of the surface morphology of the thin film product obtained in Example 1.
[0043] Figure 5aIt is a scanning transmission electron microscope image of the cross-section of the thin film product obtained in Example 1.
[0044] Figures 5b - 5f They are the elemental distribution results of the scanning transmission electron microscope energy spectrum (STEM-EDX) area scan of the cross-section of the thin film product obtained in Example 1.
[0045] Figure 6a It is a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image with atomic-level resolution at the interface of the thin film product obtained in Example 1.
[0046] Figure 6b It is a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image with atomic-level resolution at a distance of 20 nm from the interface of the thin film product obtained in Example 1.
[0047] Figure 6c It is a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image with atomic-level resolution at a distance of 40 nm from the interface of the thin film product obtained in Example 1.
[0048] Figure 7 It is the pyroelectric current switching response curve of the device based on the thin film product obtained in Example 1 to the 1064 nm laser with 3500 mW / cm 2 The ordinate is the pyroelectric current of the device.
[0049] Figure 8 It is a scanning electron microscope (SEM) photograph of the surface morphology of the thin film product obtained in Example 2.
[0050] Figure 9 It is a scanning electron microscope (SEM) image of the cross-section morphology of the thin film product obtained in Example 2.
[0051] Figure 10 It is a scanning electron microscope (SEM) image of the surface morphology of the thin film product obtained in Example 3.
[0052] Figure 11 It is a scanning electron microscope (SEM) image of the cross-section morphology of the thin film product obtained in Example 3.
[0053] Figure 12 It is a scanning electron microscope (SEM) image of the surface morphology of the thin film product obtained in Example 4.
[0054] Figure 13 It is a scanning electron microscope (SEM) image of the cross-section morphology of the thin film product obtained in Example 4.
[0055] Figure 14It is a scanning electron microscope (SEM) image of the surface morphology of the thin film product prepared in Example 5.
[0056] Figure 15 It is a scanning electron microscope (SEM) image of the cross-sectional morphology of the thin film product prepared in Example 5.
[0057] Figure 16 It is a scanning electron microscope (SEM) image of the surface morphology of the thin film product prepared in Comparative Example 1.
[0058] Figure 17 It is a scanning electron microscope (SEM) image of the surface morphology of the thin film product prepared in Comparative Example 2.
[0059] Figure 18 It is a scanning electron microscope (SEM) image of the surface morphology of the thin film product prepared in Comparative Example 3. Detailed implementation manners
[0060] To better illustrate the present invention and facilitate understanding of its technical solutions, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and do not represent or limit the scope of the protection of the present invention. The scope of protection of the present invention is subject to the claims.
[0061] In the following examples and comparative examples, reagents or instruments not indicating the manufacturer can be all conventional products that can be purchased in the market. The purity of tetrabutyl titanate, lead carbonate, strontium carbonate and potassium hydroxide is chemically pure. The size of the niobium-doped strontium titanate single crystal substrate is 10 mm × 5 mm × 0.5 mm, the orientation is <100>, and the niobium doping concentration is 0.7 wt%. The reaction kettle is a reaction kettle with a polytetrafluoroethylene inner liner and sealed by a stainless steel kit. The volume of the inner liner of the reaction kettle is 50 mL. The room temperature is 20~25°C.
[0062] Example 1
[0063] 1) Place 8.4 g of potassium hydroxide and 35 mL of deionized water in the inner liner of the polytetrafluoroethylene reaction kettle, stir well to dissolve to obtain a potassium hydroxide aqueous solution (concentration: 3.64 mol / L); while continuously stirring, add 5.5 mmol of tetrabutyl titanate to the potassium hydroxide aqueous solution in the inner liner of the reaction kettle, and stir for 30 min; then sequentially add 0.825 mmol of strontium carbonate and 5.61 mmol of lead carbonate (the molar ratio of strontium carbonate to tetrabutyl titanate is 15:100, denoted as 15% Sr) thereto, and stir well to obtain a precursor suspension;
[0064] 2) Clean the niobium-doped strontium titanate single crystal substrate successively with acetone, ethanol, and deionized water. Then fix the substrate on a polytetrafluoroethylene support and place it into the inner reactor of the autoclave containing the precursor suspension prepared in step 1). Place the inner reactor of the autoclave into the autoclave, seal it, and carry out hydrothermal reaction at 220 °C for 15 h. Then let the autoclave cool naturally to room temperature, open the autoclave, take out the product of the hydrothermal reaction, and wash the reaction product repeatedly with deionized water and absolute ethanol successively, and dry it in an oven at 60 °C to obtain the thin film product.
[0065] The thin film product obtained in the above Example 1 was tested by XRD, φ scan, TEM, EDS, HAADF-STEM (spherical aberration corrected field emission scanning transmission electron microscope) and characterized for pyroelectric response performance as follows:
[0066] The XRD pattern of this thin film product is as Figure 1 shown by the curve marked as 15%Sr in it. Each diffraction peak on this curve corresponds to the standard card (PDF#70-0746) of tetragonal PbTiO3, indicating that the crystal structure of the thin film product obtained in Example 1 is the tetragonal PbTiO3 structure and the film orientation is in the <001> direction; in addition, the diffraction angle corresponding to the diffraction peak of the (001) crystal plane has an obvious right shift relative to the standard card (PDF#70-0746) of PbTiO3.
[0067] Perform a φ scan along the <110> crystal axis direction of the film ( Figure 2 ), and a diffraction peak appears every 90° in the pattern. This result proves that the epitaxial film on the niobium-doped strontium titanate single crystal substrate is a tetragonal single crystal structure with a four-fold symmetry axis. Combining with the X-ray rocking curve ( Figure 3 ), it shows that the full width at half maximum (FWHM) of the (002) diffraction peak is 0.157°, confirming that the film has single crystal characteristics.
[0068] The SEM picture of the surface morphology of the thin film product obtained in Example 1 is as Figure 4 shown. It can be seen that the surface of this thin film product is continuous and flat. The STEM picture of the cross-section of this thin film product is as Figure 5a shown. It can be seen that the interface of this thin film product is continuous and flat, and the film thickness is 80 nm. The STEM-EDX elemental mapping results of Pb, Ti, Sr, O, and Ag elements for the selected cross-section area are respectively as Figures 5b - 5f shown. Among them, the Ag element is the metal protective layer sputtered on the surface during the preparation of the transmission sample. It can be seen from Figures 5b - 5f that in addition to the substrate, the distribution of the doping element Sr (purple signal) is detected in the epitaxial film, confirming that the element Sr is successfully incorporated into the epitaxial film.
[0069] In summary, Sr element exists in the single-crystal thin film product with a tetragonal PbTiO3 structure, and the diffraction peak of the (001) crystal plane of the thin film product shifts to the right relative to the standard card of PbTiO3, indicating that the thin film product is a lead strontium titanate single-crystal thin film.
[0070] The film interface and the interior of the film product obtained in Example 1 were characterized using a spherical aberration-corrected field emission scanning transmission electron microscope (HAADF-STEM). The HAADF-STEM images with atomic resolution at the interface, 20 nm away from the interface, and 40 nm away from the interface are shown respectively as Figure 6a , Figure 6b and Figure 6c . As can be seen from Figures 6a - 6c , the PST / Nb:STO interface is continuous, clear, atomically flat, and the lattice of the epitaxial PST film is neatly arranged.
[0071] The lead strontium titanate thin film prepared in Example 1 above was tested as follows: Ag was plated on the sample as the top electrode (the electrode had a diameter of 1 mm), and the substrate NSTO was used as the bottom electrode. Infrared light (ON) was irradiated on the sample, and after about 0.3 seconds, the infrared light was turned off (OFF). One cycle of single on and off was 0.6 seconds, and it was continuously cycled 5 times, with the whole process being 3 seconds. Infrared light with a wavelength of 1064 nm and an intensity of 3.5 W / cm 2 was selected for the test, and the corresponding pyroelectric current switching response curve is shown as Figure 7 . As can be seen from Figure 7 , when the infrared light is irradiated / turned off, the device will instantaneously generate a pyroelectric current response. The maximum value of the pyroelectric current is 66 nA, indicating that the sample responds to 1064 nm infrared light and the response is timely and sensitive.
[0072] Based on the above test results, it can be seen that: the product obtained in Example 1 is a <001>-oriented single-crystal lead strontium titanate thin film with a tetragonal PbTiO3 structure; from the microscopic morphology, the film thickness is 80 nm, with a flat and continuous film surface and an atomically flat interface. The area of the epitaxial film on the substrate is 8 mm × 5 mm, and overall it presents a large-area, single-crystal lead strontium titanate thin film with high-quality surfaces and interfaces; the thin film product obtained in Example 1 has a good response to 1064 nm infrared light and has the application prospect as a device for temperature sensing and imaging.
[0073] Example 2
[0074] 1) Place 8.4 g of potassium hydroxide and 25 mL of deionized water into the inner liner of a polytetrafluoroethylene reaction kettle, stir well to dissolve, and obtain an aqueous potassium hydroxide solution (concentration: 5.09 mol / L); with continuous stirring, add 5 mmol of tetrabutyl titanate to the aqueous potassium hydroxide solution in the inner liner of the reaction kettle, and stir for 30 min; then sequentially add 0.5 mmol of strontium carbonate and 5.4 mmol of lead carbonate (the molar ratio of strontium carbonate to tetrabutyl titanate is 10:100, denoted as 10% Sr) thereto, stir well to obtain a precursor suspension;
[0075] 2) Clean the niobium-doped strontium titanate single crystal substrate successively with acetone, ethanol, and deionized water, then fix the substrate on a polytetrafluoroethylene support, and place it into the inner liner of the reaction kettle containing the precursor suspension prepared in step 1). Place the inner liner of the reaction kettle into the reaction kettle, seal it, carry out a hydrothermal reaction at 200 °C for 18 h, then let the reaction kettle cool naturally to room temperature, remove the kettle, take out the product of the hydrothermal reaction, and then wash the reaction product repeatedly with deionized water and absolute ethanol, and dry it in an oven at 60 °C to obtain a thin film product.
[0076] Adopt the same method as in Example 1 to test the thin film product obtained in Example 2, and it is found that: the product obtained in Example 2 is a single-crystal lead strontium titanate thin film with a <001> orientation, which has a tetragonal PbTiO3 structure. The shift degree of the diffraction angle corresponding to the diffraction peak of the (001) crystal plane relative to the standard card (PDF#70-0746) of PbTiO3 is less than that of the product in Example 1, indicating that the content of Sr is lower than that in Example 1 (consistent with the reduction of Sr feeding). The XRD pattern of the thin film product obtained in Example 2 is Figure 1 the curve labeled 10% Sr in; From the microscopic morphology, the film thickness is uniform, reaching 2000 nm, having a flat and continuous film surface and an atomically flat interface. The area of the epitaxial film on the substrate is 8 mm × 5 mm, and overall it presents a large-area, micron-scale-thick single-crystal lead strontium titanate thin film with high-quality surfaces and interfaces. The SEM pictures of the surface morphology and cross-sectional morphology of the thin film product obtained in Example 2 are respectively as Figure 8 and Figure 9 shown.
[0077] Meanwhile, perform X-ray energy spectrum analysis (EDS) on the cross-section of the thin film product obtained in Example 2, and the test range is Figure 9 the area selected by the yellow frame in; The test shows that the molar ratio of Sr / (Pb + Sr) is 0.105.
[0078] Example 3
[0079] 1) Place 8.4 g of potassium hydroxide and 25 mL of deionized water in the inner liner of a polytetrafluoroethylene reaction kettle, stir well to dissolve, and obtain an aqueous potassium hydroxide solution (concentration: 5.09 mol / L); under continuous stirring, add 5 mmol of tetrabutyl titanate to the aqueous potassium hydroxide solution in the inner liner of the reaction kettle, and stir for 30 min; then sequentially add 0.25 mmol of strontium carbonate and 5.70 mmol of lead carbonate (the molar ratio of strontium carbonate to tetrabutyl titanate is 5:100, denoted as 5% Sr), stir well to obtain a precursor suspension;
[0080] 2) Clean the niobium-doped strontium titanate single crystal substrate with acetone, ethanol, and deionized water in sequence, then fix the substrate on a polytetrafluoroethylene support, and place it into the inner liner of the reaction kettle containing the precursor suspension prepared in step 1). Place the inner liner of the reaction kettle into the reaction kettle, seal it, carry out a hydrothermal reaction at 220 °C for 18 h, then let the reaction kettle cool naturally to room temperature, remove the kettle, take out the product of the hydrothermal reaction, and then wash the reaction product repeatedly with deionized water and absolute ethanol, and dry it in an oven at 60 °C to obtain a thin film product.
[0081] Adopt the same method as in Example 1 to test the thin film product obtained in Example 3, and it is found that: the product obtained in Example 3 is a single-crystal lead strontium titanate thin film with a <001> orientation, which has a tetragonal PbTiO3 structure. The shift degree of the diffraction angle corresponding to the diffraction peak of the (001) crystal plane relative to the standard card (PDF#70 - 0746) of PbTiO3 is less than that of the product in Example 2, indicating that the content of Sr is lower than that in Example 2 (consistent with the reduction of Sr feed). The XRD pattern of the thin film product obtained in Example 3 is Figure 1 the curve labeled 5% Sr in; from the microscopic morphology, the film thickness is uniform, and after measurement, the thickness is 1940 nm. It has a flat and continuous film surface and an atomically flat interface. The area of the epitaxial film on the substrate is 8 mm × 5 mm, and overall, it presents a large-area, micron-scale thick single-crystal lead strontium titanate thin film with high-quality surfaces and interfaces. The SEM images of the surface morphology and cross-sectional morphology of the thin film product obtained in Example 3 are respectively as Figure 10 and Figure 11 shown.
[0082] Meanwhile, perform X-ray energy spectrum analysis (EDS) on the cross-section of the thin film product obtained in Example 3, and the test range is Figure 11 the area selected by the yellow frame in, and the test shows that the molar ratio of Sr / (Pb + Sr) is 0.045.
[0083] Example 4
[0084] 1) Place 8.4 g of potassium hydroxide and 25 mL of deionized water in the inner liner of a polytetrafluoroethylene reaction kettle, stir well to dissolve, and obtain an aqueous potassium hydroxide solution (concentration: 5.09 mol / L); under continuous stirring, add 5 mmol of tetrabutyl titanate to the aqueous potassium hydroxide solution in the inner liner of the reaction kettle, and stir for 30 min; then sequentially add 0.15 mmol of strontium carbonate and 5.94 mmol of lead carbonate thereto (the molar ratio of strontium carbonate to tetrabutyl titanate is 3:100, denoted as 3% Sr), stir well to obtain a precursor suspension;
[0085] 2) Wash the niobium-doped strontium titanate single crystal substrate with acetone, ethanol, and deionized water in sequence, then fix the substrate on a polytetrafluoroethylene support and place it in the inner liner of the reaction kettle configured with the precursor suspension in step 1). Place the inner liner of the reaction kettle in the reaction kettle, seal it, carry out a hydrothermal reaction at 200 °C for 18 h, then let the reaction kettle cool naturally to room temperature. After unloading the kettle, take out the product of the hydrothermal reaction, wash the reaction product repeatedly with deionized water and absolute ethanol, and dry it in an oven at 60 °C to obtain a thin film product.
[0086] Adopt the same method as in Example 1 to test the thin film product obtained in Example 4, and it is found that: the product obtained in Example 4 is a single-crystal lead strontium titanate thin film with a <001> orientation, which has a tetragonal PbTiO3 structure. The shift degree of the diffraction angle corresponding to the diffraction peak of the (001) crystal plane relative to the standard card (PDF#70-0746) of PbTiO3 is less than that of the product in Example 3, indicating that the content of Sr is lower than that in Example 3 (consistent with the reduction of Sr feed). The XRD pattern of the thin film product obtained in Example 4 is Figure 1 the curve marked as 3% Sr in; from the microscopic morphology, the film thickness is uniform. After measurement, the thickness is 1060 nm, and it has a flat and continuous film surface and an atomically flat interface. The area of the epitaxial film on the substrate is 8 mm × 5 mm, and overall it presents a large-area, micron-scale-thick single-crystal lead strontium titanate thin film with high-quality surfaces and interfaces. The SEM pictures of the surface morphology and cross-sectional morphology of the thin film product obtained in Example 4 are respectively as Figure 12 and Figure 13 shown.
[0087] Meanwhile, carry out X-ray energy spectrum analysis (EDS) on the cross-section of the thin film product obtained in Example 4, and the test range is Figure 13 the area selected by the yellow frame in, and the test shows that: the molar ratio of Sr / (Pb + Sr) is 0.03.
[0088] Example 5
[0089] 1) Place 8.4 g of potassium hydroxide and 25 mL of deionized water in the inner liner of a polytetrafluoroethylene reaction kettle, stir well to dissolve, and obtain an aqueous potassium hydroxide solution (concentration: 5.09 mol / L); while continuously stirring, add 5 mmol of tetrabutyl titanate to the aqueous potassium hydroxide solution in the inner liner of the reaction kettle, and stir for 30 min; then sequentially add 0.75 mmol of strontium carbonate and 5.31 mmol of lead carbonate thereto, stir well to obtain a precursor suspension;
[0090] 2) Wash the niobium-doped strontium titanate single crystal substrate successively with acetone, ethanol and deionized water, then fix the substrate on a polytetrafluoroethylene support, and place it into the inner liner of the reaction kettle configured with the precursor suspension in step 1). Place the inner liner of the reaction kettle into the reaction kettle, seal it, carry out a hydrothermal reaction at 200 °C for 12 h, then let the reaction kettle cool naturally to room temperature, unload the kettle, take out the product of the hydrothermal reaction, and then repeatedly wash the reaction product successively with deionized water and absolute ethanol, and dry it in an oven at 60 °C to obtain a thin film product.
[0091] Adopt the same method as in Example 1 to test the thin film product obtained in Example 5, and it is found that: the product obtained in Example 5 is a single-crystal lead strontium titanate thin film with a <001> orientation, which has a tetragonal PbTiO3 structure, and the diffraction angle corresponding to the diffraction peak of the (001) crystal plane shifts to the right relative to the standard card (PDF#70-0746) of PbTiO3; from the microscopic morphology, the film thickness is uniform, and the measured thickness is 433 nm, with a flat and continuous film surface and an atomically flat interface. The area of the epitaxial film on the substrate is 8 mm × 5 mm, and overall it presents a large-area single-crystal lead strontium titanate thin film with a high-quality surface and an atomically flat interface. The SEM pictures of the surface morphology and cross-sectional morphology of the thin film product obtained in Example 5 are respectively as Figure 14 and Figure 15 shown.
[0092] Meanwhile, carry out X-ray energy spectrum analysis (EDS) on the cross-section of the thin film product obtained in Example 5, and the test range is Figure 15 the area selected by the yellow frame in
[0093] Comparative Example 1
[0094] 1) Place 8.4 g of potassium hydroxide and 25 mL of deionized water in the inner liner of a polytetrafluoroethylene reaction kettle, stir well to dissolve, and obtain an aqueous potassium hydroxide solution with a concentration of 5.09 mol / L; while stirring, continue to add 5 mmol of tetrabutyl titanate to the aqueous potassium hydroxide solution in the inner liner of the reaction kettle, and stir for 30 min; then sequentially add 0.5 mmol of strontium carbonate and 5.4 mmol of lead carbonate thereto, stir well to obtain a precursor suspension;
[0095] 2) Clean the niobium-doped strontium titanate single crystal substrate successively with acetone, ethanol and deionized water, then fix the substrate on a polytetrafluoroethylene support and place it into the inner liner of the autoclave containing the precursor suspension prepared in step 1). Place the inner liner of the autoclave into the autoclave, seal it, carry out hydrothermal reaction at 180 °C for 18 h, then let the autoclave cool naturally to room temperature, open the autoclave, take out the product of the hydrothermal reaction, wash the reaction product repeatedly with deionized water and absolute ethanol successively, and dry it in an oven at 60 °C to obtain the thin film product.
[0096] Perform scanning electron microscope analysis on the surface morphology of the thin film product prepared in Comparative Example 1 above. The SEM images are as Figure 16 shown. From Figure 16 it can be seen that the surface of the thin film is significantly discontinuous and island-like growth is remarkable.
[0097] Comparative Example 2
[0098] 1) Place 8.4 g of potassium hydroxide and 25 mL of deionized water into the inner liner of a polytetrafluoroethylene autoclave, stir well to dissolve to obtain an aqueous potassium hydroxide solution (concentration: 5.09 mol / L); with continuous stirring, add 5 mmol of tetrabutyl titanate to the aqueous potassium hydroxide solution in the inner liner of the autoclave, and stir for 30 min; then successively add 0.5 mmol of strontium carbonate and 5.4 mmol of lead carbonate thereto, and stir well to obtain a precursor suspension;
[0099] 2) Clean the niobium-doped strontium titanate single crystal substrate successively with acetone, ethanol and deionized water, then fix the substrate on a polytetrafluoroethylene support and place it into the inner liner of the autoclave containing the precursor suspension prepared in step 1). Place the inner liner of the autoclave into the autoclave, seal it, carry out hydrothermal reaction at 200 °C for 8 h, then let the autoclave cool naturally to room temperature, open the autoclave, take out the product of the hydrothermal reaction, wash the reaction product repeatedly with deionized water and absolute ethanol successively, and dry it in an oven at 60 °C to obtain the thin film product.
[0100] Perform scanning electron microscope analysis on the surface morphology of the thin film product prepared in Comparative Example 2 above. The SEM images are as Figure 17 shown. From Figure 17 it can be seen that no thin film is formed on the substrate surface, and only a small amount of particles can be observed.
[0101] Comparative Example 3
[0102] 1) Place 8.4 g of potassium hydroxide and 20 mL of deionized water into the inner liner of a polytetrafluoroethylene autoclave, stir well to dissolve to obtain an aqueous potassium hydroxide solution; with continuous stirring, add 5.5 mmol of tetrabutyl titanate to the aqueous potassium hydroxide solution in the inner liner of the autoclave, and stir for 30 min to obtain a mixed solution;
[0103] 2) Weigh 0.55 mmol of strontium nitrate and 5.94 mmol of lead nitrate, dissolve them in 10 ml of deionized water, and stir well to obtain a mixed solution.
[0104] 3) Add the mixed solution prepared in step 2) to the mixed solution prepared in 1), then add deionized water to the inner liner of the reaction kettle, and stir for 2 h to obtain a precursor suspension (the final volume is 35 ml).
[0105] 4) Wash the niobium-doped strontium titanate single crystal substrate with acetone, ethanol, and deionized water in sequence, then fix the substrate on a polytetrafluoroethylene bracket and place it in the inner liner of the reaction kettle configured with the precursor suspension in step 3). Place the inner liner of the reaction kettle in the reaction kettle, seal it, and carry out a hydrothermal reaction at 220 °C for 15 h. Then let the reaction kettle cool naturally to room temperature, unload the kettle, take out the product of the hydrothermal reaction, and wash the reaction product repeatedly with deionized water and absolute ethanol, and dry it in an oven at 60 °C to obtain a thin film product.
[0106] The surface morphology of the thin film product prepared in Comparative Example 3 above was analyzed by scanning electron microscopy, and the SEM images are as Figure 18 shown. It can be seen from Figure 18 the figure that there are many holes with different depths in the thin film.
[0107] In summary, the single-crystal lead strontium titanate thin films prepared in the embodiments of the present invention have a high-quality surface, an atomically flat interface, and a thickness that can reach the micron level, showing good pyroelectric response and meeting the material requirements of self-driven infrared detectors; at the same time, the present invention can control the film thickness and prepare micron-level high-quality and high-performance single-crystal thick films, which can facilitate the processing and production of subsequent application devices and have great industrial application value. Moreover, the preparation method of the present invention is simple, the process is easy to operate, and the raw materials are simple and easy to obtain, which is convenient for popularization.
[0108] It can be seen from this that the object of the present invention has been fully and effectively achieved. The function and structural principle of the present invention have been demonstrated and explained in the embodiments. Without departing from the above principle, the implementation manner can be modified arbitrarily. Therefore, the present invention includes all modified implementation manners based on the spirit and scope of the claims.
Claims
1. A single crystal Pb 1-x Sr x TiO3 thin film, characterized in that, It is a thin film epitaxially grown on a niobium-doped strontium titanate single crystal substrate. The thin film has a flat and continuous surface and an atomically flat interface, and the thickness of the thin film is 80-2200 nm.
2. The single-crystal Pb 1-x Sr x TiO3 thin film according to claim 1, characterized in that 0<x≤0.15。 3. The single crystal Pb 1-x Sr x Preparation method of TiO3 thin film, comprising the following steps: (1) Under stirring, tetrabutyl titanate is added to an aqueous potassium hydroxide solution and stirred thoroughly to obtain a mixed solution; then strontium carbonate and lead carbonate are successively added to the mixed solution and stirred thoroughly to obtain a precursor suspension, and the precursor suspension is placed in the inner liner of the reaction kettle. (2) The niobium-doped strontium titanate single crystal substrate is placed in the precursor suspension, and then the inner liner of the reaction kettle containing the precursor suspension is placed in the reaction kettle, sealed, and hydrothermally reacted at 200-220 °C for 12-24 h. (3) After the reaction kettle is naturally cooled, the kettle is unloaded; the product of the hydrothermal reaction is taken out, washed and dried to obtain the target thin film product.
4. The single-crystal Pb 1-x Sr x TiO3 thin film preparation method, characterized in that, In step (1), in the precursor suspension, the molar concentration of titanium element is 0.11-0.28 mol / L.
5. The single-crystal Pb 1-x Sr x preparation method of TiO3 thin film, characterized in that, In step (1), the final volume of the precursor suspension is 50-80% of the volume of the inner liner of the reaction kettle.
6. The single crystal Pb 1-x Sr x The preparation method of TiO3 thin film is characterized in that In step (1), the feeding molar ratio of strontium carbonate to tetrabutyl titanate is x:1, where 0 < x ≤ 0.
15.
7. The single crystal Pb 1-x Sr x The method for preparing TiO3 thin film is characterized in that In step (1), the feeding molar ratio of lead carbonate to tetrabutyl titanate is (1-1.5)×(1-x):
1.
8. The preparation method of the single crystal Pb 1-x Sr x TiO3 thin film, characterized in that In step (1), in the precursor suspension, the molar concentration of potassium hydroxide is 3-6 mol / L.
9. The single-crystalline Pb 1-x Sr x TiO3 thin film preparation method, characterized in that, In step (2), the orientation of the niobium-doped strontium titanate single crystal in the niobium-doped strontium titanate single crystal substrate is <100>.
10. Application of the single-crystal Pb 1-x Sr x TiO3 thin film.