Epitaxially grown kto / nsto thin films, their preparation and use

Abstract

This invention discloses epitaxially grown KTO / NSTO thin films, their preparation, and applications. The KTO epitaxial thin film possesses a large-area, continuous, and flat surface. At the KTO / NSTO heterojunction interface and within the KTO thin film, atoms are arranged regularly and neatly, without disordered or dislocation regions, and there is no significant K element deficiency. This epitaxially grown KTO / NSTO thin film is obtained through multiple hydrothermal synthesis processes. The X-ray detector fabricated using the aforementioned KTO / NSTO thin film exhibits exceptionally superior performance. At a bias voltage of 2V, a good step curve can be observed over a wide X-ray dose range, and its sensitivity and detection limit are significantly superior to current commercial X-ray detectors. Furthermore, this detector demonstrates excellent current response stability under air, high humidity, irradiation, thermal cycling, and high temperature conditions.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor devices, specifically relating to epitaxially grown single-crystal thin films and their applications, particularly in X-ray detectors. Background Technology

[0002] X-ray detectors are devices that receive X-ray radiation and convert the X-ray energy into electrical signals that can be recorded. Because X-rays have strong penetrating power and can non-destructively detect information inside objects, X-ray detectors have high spatial resolution and no detection damage, enabling accurate detection of the fine internal structures of samples such as organisms, minerals, and metals. They are widely used in medical, security, scientific research, nuclear industry, and military fields.

[0003] Based on the electrical signal conversion method, X-ray detectors are generally classified into semiconductor-type direct detectors and scintillator-type indirect detectors. Currently, the dominant type is the scintillator-type indirect detector (such as thallium-doped cesium iodide, CsI:Tl), which converts X-ray photons into low-energy photons, which are then detected by a photodetector. Due to its relatively low conversion efficiency and optical crosstalk caused by scattering, the sensitivity of this type of detector (approximately 300 μC·Gy) is limited. -1 ·cm -2 Both the X-ray conversion efficiency and imaging quality are relatively average. Semiconductor-type direct detectors, on the other hand, are based on photoconductors, such as amorphous selenium (α-Se), which directly convert X-rays into electrons, which are then collected by electrodes as electrical signals. These detectors produce soft X-ray photons (photon energy <40 keV) with good X-ray conversion efficiency and high sensitivity (approximately 440 μC·Gy). -1 ·cm -2 α-Se enables high-resolution imaging in mammography (see: Sensors, 2011, 11, 5112, Proc. SPIE 3977, 128–136, 2000). Furthermore, optical crosstalk is virtually nonexistent in semiconductor-type direct detectors. However, unfortunately, the applications of α-Se are limited due to its poor absorption of hard X-rays, low intrinsic X-ray sensitivity, and thermal decomposition above 80°C. Overall, semiconductor-type direct detectors offer higher imaging resolution and dynamic imaging capabilities, better spatial resolution, and simpler system design compared to scintillator-type indirect detectors, thus holding greater promise for future applications.

[0004] However, the scarcity of materials with high stability and excellent X-ray absorption performance limits the application of direct X-ray detectors. The light-absorbing layer, which absorbs X-rays to generate photogenerated electron-hole pairs and produces a directional photocurrent under an applied bias voltage, is the most critical part of the detector. In practical applications, different semiconductors are selected as the light-absorbing layer material depending on the specific application. Currently, the main light-absorbing layer materials for commercially available direct X-ray flat panel detectors are amorphous selenium (α-Se), silicon, and CdZnTe. These materials all possess the characteristics of highly efficient semiconductor X-ray detectors. However, these materials still have problems, including inherent defects or persistent unresolved issues in crystal growth: complex fabrication processes, high cost, and low atomic numbers leading to low sensitivity and insufficient detection dose. Therefore, developing new semiconductor materials with higher sensitivity and lower detection limits for X-rays is urgent and necessary.

[0005] In 2015, Pb-based organic-inorganic hybrid perovskite materials were first applied to X-ray detection. Since then, numerous studies on the application of halide perovskite materials in X-ray detection have been reported, demonstrating the promising application prospects of perovskite materials in high-sensitivity, low-detection-limit radiation detection. Compared to traditional CdZnTe and α-Se detectors, the high atomic numbers of lead (Pb) and halides can achieve better attenuation coefficients. Low defect density and small effective charge carrier mass can result in a large and balanced μτ product, thus effectively collecting charge. However, the weak bonding between the organic and inorganic components of organic-inorganic halide perovskite materials makes them highly susceptible to structural degradation under oxygen, heat, and moisture erosion, leading to serious stability issues in perovskite optoelectronic devices. Ion migration is prevalent in these materials, resulting in correspondingly low resistivity of the crystal material. Ion migration caused by the applied electric field during X-ray detector operation is detrimental to the control of device leakage current, leading to high detector noise levels and limiting the improvement of detector sensitivity. Meanwhile, the ion migration phenomenon induced by the applied electric field is detrimental to the long-term stability of the device. Most current organic-inorganic halide perovskite optoelectronic devices are mainly thin films with polycrystalline morphology, which have high density of defects on the surface and at grain boundaries. This reduces carrier mobility and increases the recombination probability of carriers, which will seriously affect the sensitivity, performance stability and lifespan of X-ray detectors based on organic-inorganic halide perovskite materials.

[0006] Compared to polycrystalline thin-film devices, perovskite single-crystal materials exhibit superior intrinsic properties, including higher carrier mobility, longer carrier diffusion length, and lower trap (defect state) density. This gives them outstanding photovoltaic performance and makes them ideal light-absorbing layer materials for X-ray detectors.

[0007] Current perovskite single-crystal semiconductor X-ray detectors primarily use bulk perovskite single crystals as the semiconductor light-absorbing layer material. The bulk perovskite material is in direct contact with both the top electrode and the signal readout thin-film transistor array. This detector structure has several drawbacks. First, the bulk perovskite material is prone to detachment or poor contact with the top electrode and the signal readout thin-film transistor array, leading to impaired or limited current signal transmission and difficulty in forming an effective detection signal. Second, the detector needs to maintain the highest possible output photocurrent while minimizing noise. Noise is related to the detector's dark current level, which is largely determined by the resistivity of the perovskite material itself. However, many existing perovskite materials have low resistivity, resulting in a large dark current that obliterates the signal. Furthermore, existing perovskite materials exhibit strong ion migration under an electric field, causing the dark current to be unstable over long periods. These factors contribute to a low or unstable signal-to-noise ratio. Third, existing perovskite materials often have numerous surface defects on their top and bottom surfaces, leading to severe ion migration under an applied electric field, further disrupting the dark current stability and affecting the detector's response speed. Finally, existing perovskite materials are in direct contact with the detector signal readout thin-film transistor array and the top electrode, making them prone to chemical reactions with the metal materials of the signal readout thin-film transistor array and the top electrode. This leads to a decrease in the performance of the perovskite light-absorbing layer and affects the stability of the detector performance. Moreover, the existing perovskite materials used in detectors are themselves susceptible to external conditions such as water and oxygen, which can cause chemical reactions and also affect the stability of the detector.

[0008] Meanwhile, in terms of fabrication processes, the growth of bulk perovskite single crystals is time-consuming, and large single crystals are difficult to process into the required micro-device structures, nor can they meet flexibility requirements. This limits the application and development of bulk perovskite single crystal materials. In particular, in existing halide perovskite single crystal growth methods, the crystal growth rate has always been limited by the deposition rate of solute on the crystal surface and the diffusion rate of solute in the crystal solution, and the problem of solvent evaporation during crystal growth has not been solved.

[0009] Furthermore, a common problem with currently reported X-ray detectors is the sharp increase in noise or thermal decomposition of active materials due to heat generation during device operation or high-temperature environments, leading to a drastic decline in device performance or even malfunction. For example, organic-inorganic hybrid perovskite materials have weak bonding between their organic and inorganic components, and their intrinsic material decomposition temperature is low, making them unsuitable for high-temperature environments. Moreover, reported perovskite materials exhibit high intrinsic carrier concentrations, narrow optical band gaps, low resistivity, and ion migration. As temperature increases, the intrinsic carrier concentration of semiconductor materials further increases, resistivity decreases, and ion migration becomes severe, resulting in a sharp increase in device noise and large leakage currents causing device heating. Currently, perovskite-based devices typically operate at room temperature.

[0010] In summary, developing X-ray detectors that are highly sensitive, have low detection doses, are low-cost, and exhibit high stability under various environments such as high temperature and high humidity is an important research direction in the field of X-ray detection technology. Among these, novel light-absorbing layer materials with excellent performance are crucial.

[0011] Potassium tantalate (KTaO3, abbreviated as KTO) has a typical ABO3-type perovskite structure, exhibiting no phase transition from absolute zero to its melting point (1645 K), and a relatively large band gap of approximately 3.6 eV. Currently, the two main applications of KTaO3 single crystals are: firstly, due to its high refractive index, dielectric constant, and significant secondary electro-optic effect, it can be used in capacitors, laser modulators, and tunable microwave devices; secondly, it is primarily used as a substrate material in the growth of epitaxial high-temperature superconducting thin films, ferroelectric thin films, and giant magnetoresistive thin films. However, due to the incompatibility of the low atomic numbers of K and O with the high atomic numbers required for X-ray absorbing materials; the high melting point of Ta itself, making it difficult to grow pentavalent Ta in tetravalent coordinated octahedra; the difficulty in controlling K, leading to its easy escape at high temperatures; and the generally poor high-temperature stability of conventional organic hybrid materials, there are currently no studies using KTaO3 for X-ray detectors.

[0012] Furthermore, the epitaxial growth of KTO single-crystal thin films has always been one of the challenges in material growth. When preparing KTO single-crystal thin films using conventional vapor deposition (PLD, MOCVD) methods for single-crystal thin film epitaxy, the use of SrTiO3 single-crystal substrates often results in significant strain energy at the interface due to the large lattice mismatch (~2.15%) between STO and KTO. This often leads to the growth of KTO grains with different orientations, ultimately resulting in polycrystalline thin film materials, making it impossible to obtain large-area single-crystal epitaxy. At the same time, the high temperature of vapor deposition (>600℃) easily leads to the volatilization of K, resulting in non-uniform film composition, A-site defects, and low film quality. Previously, in their earlier research, the inventors of this application successfully epitaxially grew a KTO single-crystal thin film for the first time using a hydrothermal method on a niobium-doped strontium titanate substrate. According to the disclosure in the specification of Chinese invention patent application number 201910561077.9, a single-crystal potassium tantalate thin film was epitaxially grown on a niobium-doped strontium titanate substrate with an orientation of (001). The potassium tantalate orientation was consistent with the substrate orientation, the film had a flat surface, and a thickness of 238 nm. However, this earlier research did not mention that the KTO single-crystal thin film could be used in X-ray detectors. Summary of the Invention

[0013] This invention is the first to propose using epitaxially grown KTO / NSTO thin films as a novel light-absorbing layer material for X-ray detectors. Furthermore, it overcomes the limitations of previous research, obtaining a novel epitaxial KTO / NSTO thin film with an atomically flat interface. X-ray detectors fabricated using these epitaxial KTO / NSTO thin films exhibit exceptionally superior performance: not only are good step curves observed over a wide X-ray dose range, but the device's sensitivity and detection limit are also significantly better than current commercial X-ray detectors. Simultaneously, it demonstrates excellent current response stability under air, high humidity, irradiation, thermal cycling, and high temperature conditions.

[0014] In a first aspect, the present invention provides an epitaxially grown KTO / NSTO thin film, which is a single-crystal KTO thin film epitaxially grown on an NSTO substrate, and has: a KTO / NSTO heterojunction interface that is flat at the atomic scale and has a sharp interface; an interior of the KTO thin film in which atoms are neatly arranged according to the KTO rules; and a large-area continuous and flat surface of the KTO thin film.

[0015] The sharp interface refers to the clear and distinct boundary line of the KTO / NSTO heterojunction interface, the orderly arrangement of atoms at the interface, the absence of obvious disorder and dislocations, and the absence of obvious K element deficiency.

[0016] Similarly, inside the KTO thin film, the atoms are arranged neatly according to the KTO rule, which means that there is no obvious disorder or dislocation inside the KTO thin film, nor is there any obvious lack of K element.

[0017] In some specific examples of the present invention, the thickness of the KTO thin film is 412–1200 nm.

[0018] In some specific examples of the present invention, the KTO thin film has a thickness of 852 nm.

[0019] In a second aspect, the present invention provides a method for preparing the above-described epitaxially grown KTO / NSTO thin film, comprising:

[0020] (1) Place potassium hydroxide aqueous solution and tantalum pentoxide powder in the inner liner of the first hydrothermal reactor, add deionized water, so that the volume of the reactants in the inner liner of the first hydrothermal reactor is 70-80% of the volume of the inner liner of the first hydrothermal reactor. The concentration of potassium hydroxide in the reactants is 4-10 mol / L, and the concentration of tantalum pentoxide is 0.0143-0.143 mol / L. Continue stirring for 2-3 hours to obtain a suspension of the first reaction precursor.

[0021] (2) Place the cleaned single crystal NSTO substrate on the reaction support and place it in the inner liner of the first hydrothermal reactor. Then seal it in the outer shell of the reactor and perform a hydrothermal reaction at 140-230°C for 2-24 hours to obtain a substrate with hydrothermal products grown.

[0022] (3) Place potassium hydroxide aqueous solution and tantalum pentoxide powder in the inner liner of the second hydrothermal reactor, add deionized water, so that the volume of the reactants in the inner liner of the second hydrothermal reactor is 70-80% of the volume of the inner liner of the second hydrothermal reactor. The concentration of potassium hydroxide in the reactants is 4-10 mol / L, and the concentration of tantalum pentoxide is 0.0143-0.143 mol / L. Continue stirring for 2-3 hours to obtain a suspension of the second reaction precursor.

[0023] (4) Place the substrate with hydrothermal products obtained in step (2) on the reaction support, place it in the inner liner of the second hydrothermal reactor, and then seal it in the outer shell of the reactor. Perform hydrothermal reaction at 140-230°C for 2-24 hours to obtain KTO / NSTO film.

[0024] In some specific embodiments of the present invention, the method for preparing the epitaxially grown KTO / NSTO thin film includes:

[0025] (1) Place 20 mL of potassium hydroxide aqueous solution and 2 mmol of tantalum pentoxide powder in the inner liner of the first hydrothermal reactor, add 15 mL of deionized water, so that the volume of the reactants in the inner liner of the first hydrothermal reactor is 70% of the volume of the inner liner of the first hydrothermal reactor. The concentration of potassium hydroxide in the reactants is 6 mol / L and the concentration of tantalum pentoxide is 0.057 mol / L. Continue stirring for 2 h to obtain a suspension of the first reaction precursor.

[0026] (2) The cleaned single crystal NSTO substrate is placed on the reaction support and placed in the inner liner of the first hydrothermal reactor. Then it is sealed in the outer shell of the reactor and hydrothermally reacted at 160°C for 24 hours to obtain a substrate with hydrothermal products grown.

[0027] (3) Place 20 mL of potassium hydroxide aqueous solution and 1 mmol of tantalum pentoxide powder in the inner liner of the second hydrothermal reactor, and add 15 mL of deionized water so that the volume of the reactants in the inner liner of the second hydrothermal reactor is 70% of the volume of the inner liner of the second hydrothermal reactor. The concentration of potassium hydroxide in the reactants is 6 mol / L and the concentration of tantalum pentoxide is 0.029 mol / L. Continue stirring for 2 h to obtain a suspension of the second reaction precursor.

[0028] (4) Place the substrate with hydrothermal products obtained in step (2) on the reaction support, place it in the inner liner of the second hydrothermal reactor, and then seal it in the outer shell of the reactor. Perform hydrothermal reaction at 160°C for 16 hours to obtain KTO / NSTO film.

[0029] In some specific embodiments of the present invention, the orientation of the single-crystal NSTO substrate is as follows: <100> The niobium doping concentration is 0.7 wt%.

[0030] In some specific embodiments of the present invention, the dimensions of the single-crystal NSTO substrate are 10mm × 5mm × 0.5mm.

[0031] In some specific embodiments of the present invention, the inner liner of the reactor is a polytetrafluoroethylene (PTFE) liner, the reaction support is a PTFE support, and the outer shell of the reactor is a stainless steel shell.

[0032] In some specific embodiments of the present invention, the volume of the inner liner of the first hydrothermal reactor is the same as the volume of the inner liner of the second hydrothermal reactor.

[0033] In some specific examples of the present invention, in step (4), the substrate with hydrothermal products grown in step (2) is cleaned, dried and then placed on the reaction support.

[0034] In a third aspect, the present invention provides the application of the epitaxially grown KTO / NSTO thin film in an X-ray detector, that is, the present invention provides an X-ray detector wherein the absorber layer material is the epitaxially grown KTO / NSTO thin film described above.

[0035] In some specific embodiments of the present invention, an X-ray detector adopts a longitudinal structure: Au / KTO / NSTO, wherein Au serves as the device anode and covers the surface of the KTO / NSTO thin film, and the NSTO layer of the KTO / NSTO thin film serves as the device cathode.

[0036] In some specific embodiments of the present invention, in the X-ray detector, Au is deposited on the surface of the KTO / NSTO thin film by DC sputtering.

[0037] In some specific embodiments of the present invention, the Au electrode in the X-ray detector is a circle with a diameter of 1.5 mm and a thickness of approximately 80 nm.

[0038] In addition, the epitaxially grown KTO / NSTO thin films described above can also be used in laser modulators, tunable microwave devices, or integrated optical windows.

[0039] This invention proposes for the first time the use of epitaxially grown KTO / NSTO thin films as a novel light-absorbing layer material for X-ray detectors. Unexpectedly, it was discovered that the epitaxially grown KTO / NSTO thin films obtained through multiple hydrothermal treatments possess: an atomically flat and sharp KTO / NSTO heterojunction interface; an interior KTO film with atoms arranged neatly according to KTO rules (no disordered or dislocation regions, and no significant K element deficiency); and a large-area continuous and flat KTO film surface. X-ray detectors fabricated using these large-size single-crystal KTO / NSTO thin films exhibit exceptionally high performance, for example, at a bias voltage of 2V, the X-ray absorption capacity is 39.9 nGy·s⁻¹. -1 Up to 10.53 μGy·s -1 A good step curve was observed within the X-ray dose range, with a sensitivity and detection limit of 3450.5 μC·Gy. -1 ·cm -2 and 39.9nGy·s -1 The epitaxial detection limit is 10 nGy·s -1 Furthermore, this detector exhibits excellent current response stability under conditions of air, high humidity, irradiation, thermal cycling, and high temperature, with the dark current remaining consistently around 0.04 nA. In comparison, existing X-ray detectors show the following performance: MAPbI3 single crystal achieves a sensitivity of 968.9 μC·Gy at a bias voltage of ~1V.-1 ·cm -2 The lowest detection limit of the Cs2AgBiBr6 double perovskite material is 59.7 nGy·s. -1 A flexible, printable X-ray detector based on CsPbBr3 quantum dots was successfully applied at 0.0172 mGy. air ·s -1 The sensitivity obtained under X-ray irradiation with a bias voltage of 0.1V reached 1450 μC·Gy. -1 ·cm -2 Currently, the sensitivity of commercially available α-Se semiconductor ray detectors is approximately 20 μC·Gy. -1 ·cm -2 The sensitivity of the CZT (CdZnTe) semiconductor ray detector is 318 μC·Gy. -1 ·cm -2 The detection limit is 50 nGy·s -1 Clearly, the X-ray detector of the present invention has significantly better sensitivity and detection limit than existing X-ray detectors and currently commercial X-ray detectors. Moreover, the detection limit X-ray dose of the X-ray detector of the present invention is less than one-thousandth of that of a single CT scan in current medical imaging.

[0040] Compared with the prior art, the present invention has the following beneficial technical effects:

[0041] (1) The use of epitaxially grown KTO / NSTO thin films as a new light-absorbing layer material for X-ray detectors was first proposed:

[0042] (2) It was unexpectedly discovered that the epitaxially grown KTO / NSTO thin film obtained by multiple hydrothermal treatments was a high-quality large-size single-crystal KTO thin film with an atomically flat interface. It has: an atomically flat KTO / NSTO heterojunction interface with a sharp interface; an interior of KTO thin film with atoms arranged neatly according to KTO rules (no disordered regions or dislocation regions, and no obvious loss of K element); and a large area of ​​continuous and flat KTO thin film surface.

[0043] (3) A high-performance X-ray detector was fabricated: the current response increases with the increase of the applied bias voltage; at a bias voltage of 2V, a good step curve can be observed over a very wide X-ray dose range; the sensitivity and detection limit are significantly better than existing X-ray detectors and current commercial X-ray detectors; the detection limit X-ray dose is less than one-thousandth of that in a single CT scan in current medical imaging; and compared with the lead perovskite material structure, KTO perovskite oxide is non-toxic; it exhibits excellent current response stability under air, high humidity, irradiation, thermal cycling, and high temperature environments; under various conditions, the dark current remains stable at the nA level. The X-ray detector of this invention has good application prospects in low-dose X-ray imaging, X-ray detection, and other fields, and is expected to achieve commercial application. Attached Figure Description

[0044] Figure 1 This is the XRD pattern of the final thin film product obtained in Example 1.

[0045] Figure 2 It is the KTO film (110) surface of the final thin film product obtained in Example 1. Scan the map.

[0046] Figure 3 This is an SEM image of the surface morphology of the final thin film product obtained in Example 1.

[0047] Figure 4 This is a HAADF-STEM image of the cross-sectional area of ​​the final thin film product obtained in Example 1.

[0048] Figure 5 The image shows the EDX spectra of each element in the region near the KTO / NSTO heterojunction interface of the final thin film product obtained in Example 1.

[0049] Figure 6 This is the XRD pattern of the product obtained in Comparative Example 1.

[0050] Figure 7 This is a SEM image of the surface morphology of the thin film product obtained in Comparative Example 1.

[0051] Figure 8 This is a TEM image of the cross-sectional interface of the thin film product obtained in Comparative Example 1.

[0052] Figure 9In the images, (a) and (e) are HAADF-STEM images of the cross-sections of the product obtained in Comparative Example 1 and the final thin film product obtained in Example 1; (b) and (f) are atomic-level HAADF-STEM images of the KTO / NSTO heterojunction interface in the product obtained in Comparative Example 1 and the final thin film product obtained in Example 1; (c) and (g) are HAADF-STEM images of the position corresponding to the linear disorder region extending upward perpendicular to the interface in the product obtained in Comparative Example 1 in the product obtained in Comparative Example 1 and the final thin film product obtained in Example 1; (d) and (h) are K-element energy spectra in the product obtained in Comparative Example 1 and the final thin film product obtained in Example 1, especially the K-element energy spectra of the thin film containing the position corresponding to the linear disorder region in the product obtained in Comparative Example 1.

[0053] Figure 10 This is an SEM image of the surface morphology of the final thin film product obtained in Example 2.

[0054] Figure 11 This is a SEM image of the cross-sectional area of ​​the final thin film product obtained in Example 2.

[0055] Figure 12 This is an SEM image of the surface morphology of the final thin film product obtained in Example 3.

[0056] Figure 13 This is a SEM image of the cross-sectional area of ​​the final thin film product obtained in Example 3.

[0057] Figure 14 This is a schematic diagram of the device structure of an X-ray detector.

[0058] Figure 15a and Figure 15b The results show the current response test results of the X-ray detectors to the X-ray source switch for Comparative Example 2 and Example 4, respectively.

[0059] Figure 16 The X-ray detector of Example 4 is shown to respond to X-rays at different voltages.

[0060] Figure 17a The current response of the X-ray detector of Example 4 at different X-ray doses is shown.

[0061] Figure 17b The X-ray detector of Example 4 is shown at the instrument limit dose of 39.9 nGy·s. -1 The current response under the given conditions.

[0062] Figure 18a The response current density of the X-ray detector in Example 4 is shown as a function of X-ray dose.

[0063] Figure 18b The signal-to-noise ratio of the X-ray detector in Example 4 is shown as a function of X-ray dose under a bias voltage of 2V.

[0064] Figure 18c The photocurrent and sensitivity of the X-ray detector in Example 4 are shown as a function of bias voltage.

[0065] Figure 19 The noise test results of the X-ray detector in Example 4 are shown.

[0066] Figure 20a The results show the photocurrent stability of the X-ray detector of Example 4 after prolonged exposure to an air environment (average humidity of 60%).

[0067] Figure 20b The results show the stability of the photocurrent for X-ray detection after the X-ray detector of Example 4 was tested after prolonged irradiation.

[0068] Figure 20c The results show the stability of the photocurrent of the X-ray detector in X-ray detection after exposing it to a high humidity environment.

[0069] Figure 20d The results show the stability of the photocurrent of the X-ray detector in X-ray detection after exposing the X-ray detector of Example 4 to continuous heating and cooling cycles.

[0070] Figure 20e The results show the stability of the photocurrent for X-ray detection after the X-ray detector of Example 4 was exposed to a high-temperature environment.

[0071] Figure 20f The results show the dark current stability of the X-ray detector of Example 4 under a 2V bias voltage.

[0072] Figure 21a It is a template in the shape of the "Seeking Truth Eagle" made of lead plate.

[0073] Figure 21b This is the imaging result of the X-ray detector in Example 4 under a 2V bias voltage. Detailed Implementation

[0074] 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 for illustrative purposes only and do not represent or limit the scope of protection of the present invention; the scope of protection of the present invention is defined by the claims.

[0075] Unless otherwise specified, all reagents or instruments used in the following examples and comparative examples are commercially available products.

[0076] The reactor comprises an inner liner and an outer shell. The inner liner is made of polytetrafluoroethylene (PTFE), and the outer shell is made of stainless steel. The inner liner can be removed separately. During the hydrothermal reaction, the PTFE inner liner is placed inside the stainless steel outer shell and sealed. The PTFE inner liner has good high-temperature and pressure resistance, while the sealed stainless steel outer shell, covering the inner liner, ensures that the inner liner does not deform during the reaction and maintains a high-pressure environment. In the following examples and comparative examples, the volume of the inner liner is 50 mL.

[0077] The reaction scaffold is made of polytetrafluoroethylene.

[0078] The substrate is a niobium-doped strontium titanate (Nb:SrTiO3, hereinafter abbreviated as NSTO) single crystal substrate with dimensions of 10mm × 5mm × 0.5mm and an orientation of... <100> The niobium doping concentration is 0.7 wt%. Before use, clean the substrate as follows: Adjust the height of the PTFE reaction support, place the single crystal substrate vertically in the reaction support, and place the reaction support and substrate in a 20 mL beaker. Clean the substrate ultrasonically with acetone, ethanol, water, and then ethanol in sequence. Then, place the reaction support and substrate in a forced-air drying oven at 60°C for 1 hour. The cleaned NSTO single crystal substrate is ready for use.

[0079] Example 1

[0080] 1) Weigh a certain amount of KOH (0.21 mol) and place it in the inner liner of a polytetrafluoroethylene reactor. Add 20 mL of deionized water and stir thoroughly until completely dissolved. Weigh 2 mmol of tantalum pentoxide (Ta2O5) powder and add it to the inner liner of the reactor. Add 15 mL of deionized water. At this point, the volume of the reactants in the inner liner of the reactor reaches 70% of the inner liner's volume, and the molar concentration of potassium hydroxide in the reactants is 6 mol / L. Continue stirring for 2 hours to obtain a suspension of the first reaction precursor.

[0081] 2) Place the previously cleaned and prepared NSTO single crystal substrate together with the polytetrafluoroethylene reaction support into the inner liner of the reactor, and seal the inner liner of the reactor into the outer shell of the stainless steel reactor. In an oven at 160°C, perform a hydrothermal reaction for 24 hours to grow a hydrothermal product on the NSTO single crystal substrate.

[0082] 3) After the reaction is completed, let the reactor cool naturally, open the reactor and take out the substrate with the hydrothermal product grown in the inner liner. Clean it with deionized water and ethanol 4 times and 2 times respectively, 10 minutes each time. Then place the substrate in a 60℃ drying oven for 12 hours and keep it warm as an intermediate product for later use.

[0083] 4) Weigh a certain amount of KOH (0.21 mol) and place it in a clean polytetrafluoroethylene reactor liner. Add 20 mL of deionized water and stir thoroughly until completely dissolved. Weigh 1 mmol of tantalum pentoxide (Ta2O5) powder and add it to the reactor liner. Add 15 mL of deionized water. At this point, the volume of the reactants in the reactor liner reaches 70% of the reactor liner's volume, and the molar concentration of potassium hydroxide in the reactants is 6 mol / L. Continue stirring for 2 hours to obtain a suspension of the second reaction precursor.

[0084] 5) The intermediate product obtained in step 3) together with the polytetrafluoroethylene reaction support is placed in the inner liner of the reactor in step 4), and the inner liner of the reactor is sealed in the outer shell of the stainless steel reactor. The reactor is then subjected to hydrothermal reaction at 160°C in an oven for 16 hours to obtain a substrate with the final product grown on it.

[0085] 6) After the reaction is complete, allow the reactor to cool naturally, open the reactor and remove the substrate with the final product grown in the inner liner; ultrasonically clean it 4 times with deionized water and 2 times with ethanol, each time for 10 minutes; then place the substrate in a 60℃ drying oven for 12 hours to obtain the final thin film product.

[0086] Composition, structure and morphology characterization of KTO thin films:

[0087] The final thin film product obtained in Example 1 was subjected to XRD testing, and the XRD test results are as follows: Figure 1 As shown in Figure 1, the upper and lower lines correspond to the XRD patterns of the final thin film product and the NSTO substrate, respectively. Figure 1 As can be seen, in the final thin film product, the epitaxial film is a single crystal potassium tantalate (KTO) with a cubic phase crystal structure (JCPDS 38~1470), with good crystallinity and no impurity phase peaks. The epitaxial relationship between the KTO film and the NSTO substrate is {100}KTO / / {100}NSTO.

[0088] The epitaxial KTO film (110) surface in the final product obtained in Example 1 was subjected to... Scan test, It is the angle by which the sample rotates along its normal. Scan the image as Figure 2 As shown. By Figure 2As can be seen, four diffraction characteristic peaks appear in the 0–360° range, and the interval between any two adjacent diffraction characteristic peaks is 90°, indicating that the KTO film has a four-fold symmetry axis, further verifying the cubic phase crystal structure of KTO; moreover, the intensities of the four diffraction characteristic peaks are close, indicating its good crystallinity. All the above results indicate that a single-crystal KTO film with good crystallinity was obtained. Further analysis also reveals that… Figure 2 The straight line in the middle refers to the (110) diffraction peak of KTO, which further illustrates that the epitaxial relationship between the KTO film and the NSTO substrate is {100}KTO / / {100}NSTO.

[0089] The final thin film product obtained in Example 1 was subjected to scanning electron microscopy (SEM) at 3kV, and its surface morphology is shown in the SEM image below. Figure 3 As shown. Figure 3 In the image, the thin film surface is smooth and flat without obvious defects, and the film area is 10mm×5mm. It can be seen that a large area of ​​continuous and flat single crystal KTO thin film has been epitaxially grown on the NSTO substrate.

[0090] HAADF-STEM testing was performed on the cross-sectional area of ​​the final thin film product obtained in Example 1, as shown... Figure 4 As shown. Figure 4 In the process, KTO and NSTO form a clear interface, and the thickness of the potassium tantalate film obtained after secondary hydrothermal growth is approximately 852 nm.

[0091] Furthermore, EDX analysis was performed on the cross-sectional area of ​​the final thin film product obtained in Example 1 for each element (K, Ta, Ti, Sr, and O), and the EDX spectrum is shown below. Figure 5 As shown. In Figure 5 In the corresponding original color image, K, Ta, Ti, Sr, and O elements correspond to green, red, yellow, blue, and cyan, respectively. This EDX image shows that no significant element diffusion occurred at the KTO / NSTO heterojunction interface.

[0092] In summary, the final thin film product obtained in Example 1 is a large-area continuous and smooth single-crystal KTO thin film with good crystallinity, epitaxially grown on an NSTO substrate. The film thickness is 852 nm, and the KTO / NSTO heterojunction interface is clear with no obvious element diffusion.

[0093] Comparative Example 1

[0094] 1) Weigh a certain amount of KOH (0.21 mol) and place it in the inner liner of a polytetrafluoroethylene reactor. Add 20 mL of deionized water and stir thoroughly until completely dissolved. Weigh 2 mmol of tantalum pentoxide (Ta2O5) powder and add it to the inner liner of the reactor. Add 15 mL of deionized water. At this point, the volume of the reactants in the inner liner of the reactor reaches 70% of the inner liner's volume, and the molar concentration of potassium hydroxide in the reactants is 6 mol / L. Continue stirring for 2 hours to obtain a suspension of the reaction precursor.

[0095] 2) Place the previously cleaned and prepared NSTO single crystal substrate together with the polytetrafluoroethylene reaction support into the inner liner of the reactor, and seal the inner liner of the reactor into the outer shell of the stainless steel reactor. In an oven at 160°C, perform a hydrothermal reaction for 24 hours to grow hydrothermal products on the NSTO single crystal substrate.

[0096] 3) After the reaction is completed, the reactor is allowed to cool naturally. The reactor is then opened and the substrate with hydrothermal products grown in the inner liner is removed. The substrate is ultrasonically cleaned 4 times with deionized water and 2 times with ethanol, each time for 10 minutes. The substrate is then placed in a 60°C drying oven for 12 hours to obtain the product of Comparative Example 1.

[0097] Composition, structure and morphology characterization of KTO thin films:

[0098] The products obtained in Comparative Example 1 were subjected to XRD tests, and the results are as follows: Figure 6 As shown. Figure 6 The upper and lower lines correspond to the XRD patterns of the product obtained in Comparative Example 1 and the NSTO substrate, respectively. Figure 6 As can be seen, in the product obtained in Comparative Example 1, the epitaxial film is a single crystal KTO with good crystallinity and a cubic phase crystal structure. The epitaxial relationship between the KTO film and the NSTO substrate is {100}KTO / / {100}NSTO.

[0099] The product obtained in Comparative Example 1 was subjected to scanning electron microscopy (SEM) at 3 kV. The SEM images of its surface morphology are shown below. Figure 7 As shown. Figure 7 In Comparative Example 1, the thin film surface is smooth and flat, without obvious defects, and the film area is 10 mm × 5 mm. It can be seen that a large-area, continuous, and smooth single-crystal KTO thin film was epitaxially grown on the NSTO substrate. A TEM image of the cross-section of the thin film product obtained in Comparative Example 1 is shown below. Figure 8 As shown. By Figure 8 It can be seen that the KTO film thickness is 382nm, there is a defect region at the KTO / NSTO heterojunction interface (defined by the black rectangular frame), and there are vertical linear defects extending from the KTO / NSTO heterojunction interface to the KTO surface inside the KTO film.

[0100] As can be seen, the product obtained in Comparative Example 1 is also a large-area continuous and smooth single-crystal KTO thin film epitaxially grown on an NSTO substrate, with a film thickness of 382 nm. However, unlike Example 1, in Comparative Example 1, there is an uneven region at the KTO / NSTO heterojunction interface, and there are vertical straight defects inside the epitaxial KTO thin film.

[0101] To further analyze the heterojunction interface of the products obtained in Comparative Example 1 and Example 1, the following comparative tests were performed on the product obtained in Comparative Example 1 and the final thin film product obtained in Example 1:

[0102] (i) HAADF-STEM images of the cross-section, to compare the differences in the KTO / NSTO heterojunction interface between the product obtained in Comparative Example 1 and the final thin film product obtained in Example 1, as shown below. Figure 9 As shown in (a) and (e);

[0103] (ii) HAADF-STEM images of the atomic-level interface, to compare the differences in the atomic-level structure at the KTO / NSTO heterojunction interface between the product obtained in Comparative Example 1 and the final thin film product obtained in Example 1, as shown below. Figure 9 As shown in (b) and (f);

[0104] (iii) HAADF-STEM images of the locations corresponding to the linear disorder regions extending upwards perpendicular to the interface in the product obtained in Comparative Example 1, to compare the structural differences at these locations between the product obtained in Comparative Example 1 and the final thin film product obtained in Example 1, as shown below. Figure 9 As shown in (c) and (g);

[0105] (iv) The K-element energy spectrum at the positions corresponding to the linear disorder regions extending upwards perpendicular to the interface in the product obtained in Comparative Example 1 was compared with the changes in K-element at these positions in the product obtained in Comparative Example 1 and the final thin film product obtained in Example 1, as shown below. Figure 9 As shown in (d) and (h).

[0106] according to Figure 9 In (a) to (d), the products obtained in Comparative Example 1 show a large number of disordered regions near the interface (see...). Figure 9 In the high-resolution image of HAADF-STEM, the black area near the interface (a) appears as a region with poor interface quality, and there are also a large number of vertically extending disordered regions extending upwards from the interface (see...). Figure 9 (The black arrow in (a)). Figure 9In (b), further analysis of the black region near the interface at atomic resolution revealed that some parts of the black region lacked obvious atomic arrangement structure, while others tended to have an atomic arrangement similar to that of KTO structure. Figure 9 Further analysis of the vertically oriented disordered region at atomic resolution (c) revealed that no obvious atomic arrangement was observed in this region either. Combined with... Figure 9 Energy dispersive spectroscopy (EDS) analysis of K in region (d) shows that the K content in this region is low (white arrow). Therefore, it can be inferred that the formation of the vertically shaped disordered region is due to the absence of K in this region, which prevents it from exhibiting the regular atomic arrangement of KTO, thus resulting in a disordered structure.

[0107] according to Figure 9 In the final thin film products obtained in Example 1, from (e) to (h), Figure 9 In (e), it is visible that there is no disorder region at the interface. At the positions corresponding to the disorder region in the product obtained in Comparative Example 1 and the vertical disorder region inside the film, the disorder region has completely disappeared. Figure 9 Further analysis of the heterojunction interface in (f) revealed that the atoms at the interface are arranged in a regular pattern (the position corresponding to the disorder region at the interface in Comparative Example 1 is also arranged in a regular pattern), the boundary line of the interface is clear, and it also presents a high-quality sharp interface at the atomic scale. Figure 9 Further analysis of the film interior (g) revealed that all atoms were arranged regularly according to the KTO structure. Combined with the K element energy spectrum analysis in Figure 9 (h), no significant K element deficiency was observed. At the locations corresponding to the vertically shaped disordered regions inside the film in Comparative Example 1, the atoms were arranged regularly according to the KTO structure. Figure 9 Energy spectrum analysis of K element in (h) shows that there is no obvious deficiency of K element at this location.

[0108] In summary, it can be observed that compared to Comparative Example 1, the KTO / NSTO heterojunction interface quality and the internal quality of the epitaxial KTO film of the final thin film product obtained in Example 1 were significantly improved. At positions corresponding to the disordered regions at the interface and the vertically shaped disordered regions inside the film in Comparative Example 1, the atoms in the final thin film product obtained in Example 1 were neatly arranged, and there was no significant deficiency of the K element. That is, in both the KTO / NSTO heterojunction interface and the internal quality of the epitaxial KTO film of the final thin film product obtained in Example 1, the atoms were neatly arranged in a regular pattern, with no obvious disordered or dislocation regions, and no significant deficiency of the K element.

[0109] Example 2

[0110] 1) Weigh a certain amount of KOH (0.21 mol) and place it in the inner liner of a polytetrafluoroethylene reactor. Add 20 mL of deionized water and stir thoroughly until completely dissolved. Weigh 1 mmol of tantalum pentoxide (Ta2O5) powder and add it to the inner liner of the reactor. Add 15 mL of deionized water. At this point, the volume of the reactants in the inner liner of the reactor reaches 70% of the inner liner's volume, and the molar concentration of potassium hydroxide in the reactants is 6 mol / L. Continue stirring for 2 hours to obtain a suspension of the first reaction precursor.

[0111] 2) Place the previously cleaned and prepared NSTO single crystal substrate together with the polytetrafluoroethylene reaction support into the inner liner of the reactor, and seal the inner liner of the reactor into the outer shell of the stainless steel reactor. In an oven at 160°C, perform a hydrothermal reaction for 24 hours to grow a hydrothermal product on the NSTO single crystal substrate.

[0112] 3) After the reaction is completed, let the reactor cool naturally, open the reactor and take out the substrate with the hydrothermal product grown in the inner liner. Clean it with deionized water and ethanol 4 times and 2 times respectively, 10 minutes each time. Then place the substrate in a 60℃ drying oven for 12 hours and keep it warm as an intermediate product for later use.

[0113] 4) Weigh a certain amount of KOH (0.21 mol) and place it in a clean polytetrafluoroethylene reactor liner. Add 20 mL of deionized water and stir thoroughly until completely dissolved. Weigh 0.5 mmol of tantalum pentoxide (Ta2O5) powder and add it to the reactor liner. Add 15 mL of deionized water. At this point, the volume of the reactants in the reactor liner reaches 70% of the reactor liner volume, and the molar concentration of potassium hydroxide in the reactants is 6 mol / L. Continue stirring for 2 hours to obtain a suspension of the second reaction precursor.

[0114] 5) The intermediate product obtained in step 3) together with the polytetrafluoroethylene reaction support is placed in the inner liner of the reactor in step 4), and the inner liner of the reactor is sealed in the outer shell of the stainless steel reactor. The reactor is then subjected to hydrothermal reaction at 160°C in an oven for 16 hours to obtain a substrate with the final product grown on it.

[0115] 6) After the reaction is complete, allow the reactor to cool naturally, open the reactor and remove the substrate with the final product grown in the inner liner; ultrasonically clean it 4 times with deionized water and 2 times with ethanol, each time for 10 minutes; then place the substrate in a 60℃ drying oven for 12 hours to obtain the final thin film product.

[0116] SEM analysis of the film surface morphology showed that it was smooth and flat with no obvious defects. The film area was 10 mm × 5 mm. Figure 10 As shown in the figure. SEM images of the cross-sectional area of ​​the thin film show that KTO and NSTO form a clear interface. The thickness of the potassium tantalate film obtained after secondary hydrothermal growth is approximately 427 nm. Figure 11 As shown.

[0117] Example 3

[0118] 1) Weigh a certain amount of KOH (0.21 mol) and place it in the inner liner of a polytetrafluoroethylene reactor. Add 20 mL of deionized water and stir thoroughly until completely dissolved. Weigh 1 mmol of tantalum pentoxide (Ta2O5) powder and add it to the inner liner of the reactor. Add 15 mL of deionized water. At this point, the volume of the reactants in the inner liner of the reactor reaches 70% of the inner liner's volume, and the molar concentration of potassium hydroxide in the reactants is 6 mol / L. Continue stirring for 2 hours to obtain a suspension of the first reaction precursor.

[0119] 2) Place the previously cleaned and prepared NSTO single crystal substrate together with the polytetrafluoroethylene reaction support into the inner liner of the reactor, and seal the inner liner of the reactor into the outer shell of the stainless steel reactor. In an oven at 160°C, perform a hydrothermal reaction for 24 hours to grow a hydrothermal product on the NSTO single crystal substrate.

[0120] 3) After the reaction is completed, let the reactor cool naturally, open the reactor and take out the substrate with the hydrothermal product grown in the inner liner. Clean it with deionized water and ethanol 4 times and 2 times respectively, 10 minutes each time. Then place the substrate in a 60℃ drying oven for 12 hours and keep it warm as an intermediate product for later use.

[0121] 4) Weigh a certain amount of KOH (0.21 mol) and place it in a clean polytetrafluoroethylene reactor liner. Add 20 mL of deionized water and stir thoroughly until completely dissolved. Weigh 1 mmol of tantalum pentoxide (Ta2O5) powder and add it to the reactor liner. Add 15 mL of deionized water. At this point, the volume of the reactants in the reactor liner reaches 70% of the reactor liner's volume, and the molar concentration of potassium hydroxide in the reactants is 6 mol / L. Continue stirring for 2 hours to obtain a suspension of the second reaction precursor.

[0122] 5) The intermediate product obtained in step 3) together with the polytetrafluoroethylene reaction support is placed in the inner liner of the reactor in step 4), and the inner liner of the reactor is sealed in the outer shell of the stainless steel reactor. The reactor is then subjected to hydrothermal reaction at 160°C in an oven for 16 hours to obtain a substrate with the final product grown on it.

[0123] 6) After the reaction is complete, allow the reactor to cool naturally, open the reactor and remove the substrate with the final product grown in the inner liner; ultrasonically clean it 4 times with deionized water and 2 times with ethanol, each time for 10 minutes; then place the substrate in a 60℃ drying oven for 12 hours to obtain the final thin film product.

[0124] SEM analysis of the film surface morphology showed that it was smooth and flat with no obvious defects. The film area was 10 mm × 5 mm. Figure 12 As shown in the figure. SEM images of the cross-sectional area of ​​the thin film show that KTO and NSTO form a clear interface. The thickness of the potassium tantalate film obtained after secondary hydrothermal growth is approximately 743 nm. Figure 13 As shown.

[0125] Example 4: Fabrication of an X-ray Detector

[0126] The X-ray detector employs a vertical "sandwich" structure: Au / KTO / NSTO. Au serves as the anode, deposited on the KTO / NSTO thin film prepared in Example 1 via DC sputtering. The Au electrode is a circle with a diameter of 1.5 mm and a thickness of approximately 80 nm. The NSTO layer of the KTO / NSTO thin film serves as the cathode, with X-rays incident from the Au electrode side. The detector structure is as follows: Figure 14 As shown. The applied bias voltage is 2V.

[0127] Comparative Example 2

[0128] It is basically the same as Example 4, except that the KTO / NSTO film was prepared by Comparative Example 1.

[0129] To compare the performance of X-ray detectors fabricated with thin films having different microstructures, current response tests were performed with X-ray source switching on both the X-ray detector prepared in Comparative Example 2 and the X-ray detector prepared in Example 4, with an X-ray dose of 10.53 μGy·s. -1 The results are as follows: Figure 15a and Figure 15b As shown.

[0130] Figure 15a In the comparison, the X-ray detector prepared by Comparative Example 2 showed good step response, with rapid step rise and fall, indicating that the KTO film can absorb X-ray energy and generate current under bias voltage; however, the light and dark currents of the X-ray detector were unstable, exhibiting sawtooth jitter, and the signal-to-noise ratio was low (about 20), so it can be basically determined that it cannot be used in practice.

[0131] Figure 15bIn this study, the X-ray detector prepared by Example 4 exhibited good step response, with fast and flat step rise and fall speeds. The device's light and dark currents remained stable, with the dark current stabilizing at around 0.04 nA, and the signal-to-noise ratio exceeding 300.

[0132] It is evident that the KTO thin-film detector in Example 4 exhibits significantly different X-ray detection performance compared to Comparative Example 2, and is far superior to Comparative Example 2. In particular, its high signal-to-noise ratio means that it can achieve high imaging resolution, which is expected to be practically applicable.

[0133] To further explore other performance characteristics of the X-ray detector prepared in Example 4, the following performance tests were conducted:

[0134] X-ray detector bias voltage response: To test the device's response to X-rays under different voltages, the current of the device was measured by continuously switching the X-ray source on and off in air using the X-ray detector of Example 4, with the X-ray dose maintained at 10.53 μGy·s. -1 The result remains unchanged. Figure 16 As shown.

[0135] Figure 16 In the experiment, as the voltage increased from 0.5V to 2V, the device's dark current remained consistently around 0.04nA, maintaining a remarkably stable level. This stable and low dark current allows for a higher signal-to-noise ratio and a lower detection limit for the detector. Secondly, with continuous switching of the X-ray source, the device current exhibited a sharp, step-like response, with rapid and relatively flat rises and falls, indicating a fast and stable X-ray response. Furthermore, as the voltage increased, the photocurrent also increased, rising from 0.25nA to 1.09nA from 0.5V to 2V, meaning that a higher voltage resulted in a larger response current. Simultaneously, the increase in photocurrent slowed down from 1.5V to 2V, indicating that the absorption of X-rays by the KTO layer in the device gradually approached saturation. Since the KTO layer is much thinner than the bulk material, the internal electric field of the device reached a very high level, reaching 3.28 × 10⁻⁶ at 2V. 4 V / cm. It is evident that within the voltage range that the KTO thin-film X-ray detector can withstand, the higher the voltage, the greater the obtained response current, which is crucial for device applications.

[0136] Lower dose limit of X-ray detectors: For X-ray detectors, sensitivity and detection limit are very important performance indicators, so it is necessary to test the current response of the device under different X-ray doses.

[0137] In the X-ray detector of Example 4, an external bias voltage of 2V was applied. By adjusting the current inside the X-ray source and adding metal attenuators of different thicknesses, the current response of the device to different X-ray doses was tested under a series of metrological gradients. The results are as follows: Figure 17a As shown. Figure 17a In the middle, when the X-ray dose is 10.53 μGy·s -1 It continued to decrease to 574.9 nGy·s -1 In both cases, a step curve of the device with the switching of the X-ray source could be observed, with the current decreasing from 1.1 nA to 0.28 nA, while the dark current remained stable at around 0.04 nA.

[0138] Figure 17b The current response of the device under the instrument's detection limit dose is presented. Figure 17b In the middle, when the X-ray dose is the instrument's maximum dose of 39.9 nGy·s -1 At this point, the dose decreased by nearly 1000 times compared to the initial detection X-ray. At this time, the device still had a good continuous step curve and the dark current remained stable. The calculated signal-to-noise ratio of the device response was 20.7, which is already a considerable result.

[0139] Based on the detector current response data under different X-ray doses, the detector response current density and signal-to-noise ratio (SNR) are calculated. The changes in detector response current density with X-ray dose and the changes in SNR with X-ray dose under a 2V bias voltage are presented, respectively. Figure 18a and Figure 18b As shown.

[0140] according to Figure 18a As the X-ray dose increases, the response current density exhibits a roughly linear change. Furthermore, the device sensitivity is calculated using the formula S = I / (A × D) (S: device sensitivity to X-rays, I: photocurrent, D: X-ray dose, A: effective X-ray receiving area of ​​the device). The result is that when the bias voltage is 2V, the device sensitivity is 3450.5 μC·Gy. -1 ·cm -2 Simultaneously, based on the experimental results, we extended the observations and found that when the signal-to-noise ratio (SNR) was as low as 3 (the international standard minimum detection SNR is 3), the X-ray dose was 10 nGy·s. -1 That is, the epitaxial detection limit is 10 nGy·s -1 .

[0141] Currently, the sensitivity of commercially available α-Se semiconductor ray detectors is 20 μC·Gy. -1 ·cm -2 The sensitivity of the CZT (CdZnTe) semiconductor ray detector is 318 μC·Gy.-1 ·cm -2 The detection limit is 50 nGy·s -1 It is evident that the sensitivity and detection limit of the X-ray detector in this embodiment are significantly superior to those of current commercial X-ray detectors. Moreover, the detection limit X-ray dose of the X-ray detector in this embodiment is less than one-thousandth of that of a single CT scan in current medical imaging, indicating that KTO films have high potential in low-dose X-ray imaging, X-ray detection, and other fields.

[0142] according to Figure 18b As the X-ray radiation dose increases, the signal-to-noise ratio of the device also increases accordingly, and the rate of increase accelerates; at 10 μGy·s -1 At X-ray doses, the device's signal-to-noise ratio is higher than 300, which is beneficial for obtaining high imaging resolution and achieving high-quality imaging.

[0143] Figure 18c The changes in photocurrent and sensitivity of the device with bias voltage were shown, revealing that the response current and sensitivity gradually increase with increasing bias voltage; even with a bias voltage of only 0.5V, the device's sensitivity reaches 700 μC·Gy. -1 ·cm -2 about.

[0144] Noise testing of X-ray detectors: Noise is a crucial indicator for detector devices, characterizing the stability and fluctuation range of the signal. It is typically determined by internal defects, crystal quality, and electrode contact. Noise testing was performed on the X-ray detector of Example 4, and the results are as follows... Figure 19 As shown in the figure, the noise of this device does not change significantly with frequency, and the noise level is around 10. ～13 A Hz ～1 / 2 This indicates that the noise type is white noise, mainly contributed by the testing instrument itself and shot noise within the device. This also demonstrates the high signal stability of the potassium tantalate X-ray detector.

[0145] X-ray detector stability: A 2V external bias voltage was applied to the X-ray detector of Example 4, and various stability tests were performed on the device, including the stability of the X-ray detection photocurrent after exposure to air, the stability of the X-ray detection photocurrent after long-term radiation exposure, the stability of the X-ray detection photocurrent after exposure to high humidity, the stability of the X-ray detection photocurrent after continuous thermal cycling, the stability of the X-ray detection photocurrent after exposure to high temperature, and the stability of the device's dark current. The test results are as follows: Figures 20a to 20f As shown.

[0146] like Figure 20a As shown, we placed the X-ray detector of Example 4 in an indoor environment with an average humidity of 60% for 1800 hours and intermittently tested its X-ray current response capability during this period. We found that the photocurrent remained within a small range of fluctuation during these 1800 hours, which indicates that the device performance did not significantly degrade during the test and that the air stability was good.

[0147] like Figure 20b As shown, we placed the X-ray detector from Example 4 very close to the radiation source and subjected it to radiation for 48 hours at a dose of 10.53 μGy·s. -1 The cumulative dose was 1819.584 mGy, equivalent to more than 40,000 CT scans. According to... Figure 20b As shown, under 48 hours of radiation, the device response only fluctuated slightly and did not decrease significantly. The two dashed lines represent: the radiation source was temporarily shut down for 15 minutes due to instrument overheating, and the radiation source was shut down during a power outage at night. The shutdown time was included in the irradiation time. The test results indicate that the KTO device has good current response stability under irradiation conditions, and 48 hours of radiation did not cause significant damage to the KTO crystal.

[0148] To verify its current response stability under high humidity conditions, we extremely immersed the X-ray detector of Example 4 directly in pure water for a total immersion time of 240 hours. Figure 20c As shown in the illustration. During the immersion process, the device was removed daily for drying and then subjected to X-ray response testing. After the testing was completed, it was immersed in water again. Figure 20c As shown, the device's X-ray response performance did not decrease significantly during the immersion process, indicating that the detector has the potential to operate in high humidity environments.

[0149] To verify the device's sensitivity to temperature changes and the stability of its current response during switching between high and low temperature environments, we placed the X-ray detector from Example 4 on a temperature-changing stage and set a hot-cold temperature cycle lasting 820 seconds. Figure 20d As shown in the illustration, specifically, the temperature of the variable-temperature stage was first cooled from room temperature to ~40°C. After the temperature stabilized, the cycle began. The temperature was first uniformly increased from ~40°C to 70°C over 110 seconds; then maintained at 70°C for 300 seconds; then uniformly decreased to ~40°C over 110 seconds, and maintained at ~40°C for 300 seconds, which constituted one complete cycle. After each cycle, the device was removed for X-ray response testing. The test results are as follows: Figure 20dAs shown, after 20 temperature cycles, the device performance decreased slightly, but it was still close to 80% of the initial response strength. During the test, we observed that the gold electrode on the KTO turned slightly white as the cycle progressed. Therefore, it can be considered that the slight decrease in device performance was due to the electrode rather than the KTO: the metal electrode expands and contracts in volume during the temperature change, resulting in poor contact with the KTO.

[0150] Furthermore, we tested the device's high-temperature tolerance. We placed the device on a 200°C hot stage for 40 hours, removing it periodically for X-ray response testing, and then placing it back on the hot stage after each test. The test results are as follows: Figure 20e As shown, even after being placed on a hot stage at 200°C for 40 hours, the photocurrent of the device did not decrease significantly, indicating that it has excellent thermal stability and the potential to perform detection work in high-temperature environments.

[0151] In addition to testing the photocurrent stability of the device under various conditions, we also tested its dark current stability under a 2V bias. We connected the device in a circuit and used a Keithley 2400 source meter to record its dark current in real time. After 46 hours of continuous testing, as shown... Figure 20f As shown, we can see that the dark current remains very stable, always around 0.04 nA.

[0152] Based on the above six stability characterization results, we believe that the X-ray detector prepared in Example 4 has excellent current response stability under air, high humidity, irradiation, thermal cycling, and high temperature environments, and the dark current remains stable during long-term operation.

[0153] Imaging Test of X-ray Detector: As the foregoing research shows, the X-ray detector in Example 4 possesses extremely low dark current and a highly stable signal-to-noise ratio, ensuring the acquisition of a stable photocurrent output signal, which holds promise for imaging applications. To verify the detector's potential in imaging applications, we fabricated a template in the shape of a "Seeking Truth Eagle" using lead plates (e.g., Figure 21a (As shown), and sandwiched between two pieces of cardboard. During imaging, the cardboard with the "Seeking Truth Eagle" inscription was placed between the X-ray source and the detector, using a dose of approximately 200 μGy·s. -1 The device was biased at 2V, and imaging tests were performed using a point scan method. The test results are as follows: Figure 21b As shown. Figure 21a The shape of the "Seeking Truth Eagle" is clearly presented in the image. Figure 21b middle, Figure 21bThe original color image clearly shows that the resulting image has excellent color contrast, indicating that the KTO thin-film X-ray detector performs well in imaging applications. Furthermore, by reducing pixel size and test distance, spatial resolution can be further improved, enabling higher-resolution imaging applications.

[0154] In addition, the KTO / NSTO thin films prepared in Examples 2 and 3 were also used to prepare X-ray detectors in the same way as in Example 4. They all showed good step response similar to that in Example 1, with fast and flat step rise and fall speeds. The light and dark currents of the devices were stable, and the response currents were in the nA range.

[0155] Therefore, it is evident that the objective of this invention has been fully and effectively achieved. The function and structural principles of this invention have been demonstrated and explained in the embodiments. Any modifications can be made to the implementation methods without departing from the stated principles. Therefore, this invention includes all modified embodiments based on the spirit and scope of the claims.

Claims

1. An application of an epitaxially grown KTO / NSTO thin film, characterized in that, The application involves using the epitaxially grown KTO / NSTO thin film in an X-ray detector. The epitaxially grown KTO / NSTO thin film is prepared by the following method: (1) Place potassium hydroxide aqueous solution and tantalum pentoxide powder in the inner liner of the first hydrothermal reactor, add deionized water, so that the volume of the reactants in the inner liner of the first hydrothermal reactor is 70-80% of the volume of the inner liner of the first hydrothermal reactor. The concentration of potassium hydroxide in the reactants is 4-10 mol / L, and the concentration of tantalum pentoxide is 0.0143-0.143 mol / L. Continue stirring for 2-3 hours to obtain a suspension of the first reaction precursor. (2) Place the cleaned single crystal NSTO substrate on the reaction support and place it in the inner liner of the first hydrothermal reactor. Then seal it in the outer shell of the reactor and perform hydrothermal reaction at 140~230℃ for 2~24h to obtain a substrate with hydrothermal products grown. (3) Place potassium hydroxide aqueous solution and tantalum pentoxide powder in the inner liner of the second hydrothermal reactor, add deionized water, so that the volume of the reactants in the inner liner of the second hydrothermal reactor is 70-80% of the volume of the inner liner of the second hydrothermal reactor. The concentration of potassium hydroxide in the reactants is 4-10 mol / L, and the concentration of tantalum pentoxide is 0.0143-0.143 mol / L. Continue stirring for 2-3 hours to obtain a suspension of the second reaction precursor. (4) Place the substrate with hydrothermal products obtained in step (2) on the reaction support, place it in the inner liner of the second hydrothermal reactor, and then seal it in the outer shell of the reactor. Perform hydrothermal reaction at 140~230℃ for 2~24h to obtain KTO / NSTO film.

2. The application of the epitaxially grown KTO / NSTO thin film as described in claim 1, characterized in that, The epitaxially grown KTO / NSTO thin film was prepared by the following method: (1) Place 20 mL of potassium hydroxide aqueous solution and 2 mmol of tantalum pentoxide powder in the inner liner of the first hydrothermal reactor, add 15 mL of deionized water, so that the volume of the reactants in the inner liner of the first hydrothermal reactor is 70% of the volume of the inner liner of the first hydrothermal reactor. The concentration of potassium hydroxide in the reactants is 6 mol / L and the concentration of tantalum pentoxide is 0.057 mol / L. Continue stirring for 2 h to obtain a suspension of the first reaction precursor. (2) The cleaned single crystal NSTO substrate is placed on the reaction support and placed in the inner liner of the first hydrothermal reactor. Then it is sealed in the outer shell of the reactor and hydrothermally reacted at 160°C for 24 hours to obtain a substrate with hydrothermal products grown. (3) Place 20 mL of potassium hydroxide aqueous solution and 1 mmol of tantalum pentoxide powder in the inner liner of the second hydrothermal reactor, add 15 mL of deionized water, so that the volume of the reactants in the inner liner of the second hydrothermal reactor is 70% of the volume of the inner liner of the second hydrothermal reactor. The concentration of potassium hydroxide in the reactants is 6 mol / L and the concentration of tantalum pentoxide is 0.029 mol / L. Continue stirring for 2 h to obtain a suspension of the second reaction precursor. (4) Place the substrate with hydrothermal products obtained in step (2) on the reaction support, place it in the inner liner of the second hydrothermal reactor, and then seal it in the outer shell of the reactor. Perform hydrothermal reaction at 160°C for 16 hours to obtain KTO / NSTO film.

3. The application of the epitaxially grown KTO / NSTO thin film as described in claim 1, characterized in that, The orientation of the single-crystal NSTO substrate is as follows: <100> The niobium doping concentration is 0.7 wt%.

4. The application of the epitaxially grown KTO / NSTO thin film as described in claim 1, characterized in that, The epitaxially grown KTO / NSTO thin film is a single-crystal KTO thin film epitaxially grown on an NSTO substrate, and has: a flat KTO / NSTO heterojunction interface at the atomic scale with a sharp interface; an interior of the KTO thin film with atoms arranged neatly according to the KTO rules; and a large-area continuous and flat KTO thin film surface.

5. The application of the epitaxially grown KTO / NSTO thin film as described in claim 1, characterized in that, The thickness of the KTO thin film is 412 nm to 1200 nm.

6. The application of the epitaxially grown KTO / NSTO thin film as described in claim 1, characterized in that, The KTO thin film has a thickness of 852 nm.

7. An X-ray detector, characterized in that, The absorber layer material is an epitaxially grown KTO / NSTO thin film prepared by the following method: (1) Place potassium hydroxide aqueous solution and tantalum pentoxide powder in the inner liner of the first hydrothermal reactor, add deionized water, so that the volume of the reactants in the inner liner of the first hydrothermal reactor is 70-80% of the volume of the inner liner of the first hydrothermal reactor. The concentration of potassium hydroxide in the reactants is 4-10 mol / L, and the concentration of tantalum pentoxide is 0.0143-0.143 mol / L. Continue stirring for 2-3 hours to obtain a suspension of the first reaction precursor. (2) Place the cleaned single crystal NSTO substrate on the reaction support and place it in the inner liner of the first hydrothermal reactor. Then seal it in the outer shell of the reactor and perform hydrothermal reaction at 140~230℃ for 2~24h to obtain a substrate with hydrothermal products grown. (3) Place potassium hydroxide aqueous solution and tantalum pentoxide powder in the inner liner of the second hydrothermal reactor, add deionized water, so that the volume of the reactants in the inner liner of the second hydrothermal reactor is 70-80% of the volume of the inner liner of the second hydrothermal reactor. The concentration of potassium hydroxide in the reactants is 4-10 mol / L, and the concentration of tantalum pentoxide is 0.0143-0.143 mol / L. Continue stirring for 2-3 hours to obtain a suspension of the second reaction precursor. (4) Place the substrate with hydrothermal products obtained in step (2) on the reaction support, place it in the inner liner of the second hydrothermal reactor, and then seal it in the outer shell of the reactor. Perform hydrothermal reaction at 140~230℃ for 2~24h to obtain KTO / NSTO film.

8. The X-ray detector as claimed in claim 7, characterized in that, The epitaxially grown KTO / NSTO thin film was prepared by the following method: (1) Place 20 mL of potassium hydroxide aqueous solution and 2 mmol of tantalum pentoxide powder in the inner liner of the first hydrothermal reactor, add 15 mL of deionized water, so that the volume of the reactants in the inner liner of the first hydrothermal reactor is 70% of the volume of the inner liner of the first hydrothermal reactor. The concentration of potassium hydroxide in the reactants is 6 mol / L and the concentration of tantalum pentoxide is 0.057 mol / L. Continue stirring for 2 h to obtain a suspension of the first reaction precursor. (2) The cleaned single crystal NSTO substrate is placed on the reaction support and placed in the inner liner of the first hydrothermal reactor. Then it is sealed in the outer shell of the reactor and hydrothermally reacted at 160°C for 24 hours to obtain a substrate with hydrothermal products grown. (3) Place 20 mL of potassium hydroxide aqueous solution and 1 mmol of tantalum pentoxide powder in the inner liner of the second hydrothermal reactor, add 15 mL of deionized water, so that the volume of the reactants in the inner liner of the second hydrothermal reactor is 70% of the volume of the inner liner of the second hydrothermal reactor. The concentration of potassium hydroxide in the reactants is 6 mol / L and the concentration of tantalum pentoxide is 0.029 mol / L. Continue stirring for 2 h to obtain a suspension of the second reaction precursor. (4) Place the substrate with hydrothermal products obtained in step (2) on the reaction support, place it in the inner liner of the second hydrothermal reactor, and then seal it in the outer shell of the reactor. Perform hydrothermal reaction at 160°C for 16 hours to obtain KTO / NSTO film.

9. The X-ray detector as claimed in claim 7, characterized in that, The orientation of the single-crystal NSTO substrate is as follows: <100> The niobium doping concentration is 0.7 wt%.

10. The X-ray detector as claimed in claim 7, characterized in that, The epitaxially grown KTO / NSTO thin film is a single-crystal KTO thin film epitaxially grown on an NSTO substrate, and has: a flat KTO / NSTO heterojunction interface at the atomic scale with a sharp interface; an interior of the KTO thin film with atoms arranged neatly according to the KTO rules; and a large-area continuous and flat KTO thin film surface.

11. The X-ray detector as claimed in claim 7, characterized in that, The thickness of the KTO thin film is 412 nm to 1200 nm.

12. The X-ray detector as claimed in claim 7, characterized in that, The KTO thin film has a thickness of 852 nm.

13. The X-ray detector according to any one of claims 7 to 12, characterized in that, The X-ray detector adopts a vertical structure: Au / KTO / NSTO, wherein Au serves as the device anode and covers the surface of the KTO / NSTO thin film, and the NSTO layer of the KTO / NSTO thin film serves as the device cathode.

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