Solution method preparation and X-ray detection application of ethyl p-hydroxybenzoate single crystal

Abstract

The invention discloses solution method preparation and X-ray detection application of an ethyl p-hydroxybenzoate single crystal, and relates to the technical field of organic crystals. The method comprises the following steps: dissolving ethyl p-hydroxybenzoate powder in acetone, then adding petroleum ether to form a mixed solution, and then volatilizing the solution to obtain a seed crystal; placing the seed crystal in an acetone solution, placing the acetone solution in a sealed container, and carrying out crystal growth at 0-5 DEG C to obtain a large-size crystal; and cutting the large-size crystal along a crystal cleavage surface to obtain the ethyl p-hydroxybenzoate single crystal with a flat surface. According to the invention, the solution method preparation of the ethyl p-hydroxybenzoate large-size crystal is realized for the first time, the ethyl p-hydroxybenzoate large-size crystal is applied to direct X-ray detection, and a new technical scheme is provided for solving the problems of high cost, complex preparation and the like of a traditional detection material.

Description

Technical Field

[0001] This invention relates to the field of organic crystal technology, specifically to a solution-based preparation of ethyl p-hydroxybenzoate single crystals and its application in X-ray detection. Background Technology

[0002] X-ray detection technology is core to medical imaging, security inspection, and industrial non-destructive testing. Currently, the mainstream technologies are divided into indirect and direct detection. Indirect detection converts X-rays into visible light using a scintillator, which is then detected by a photoelectric sensor; its spatial resolution is limited by light scattering effects. Direct detection utilizes semiconductor materials to directly ionize X-rays, generating electron-hole pairs, and collects the charges using an external electric field to form an electrical signal. Theoretically, it has higher spatial resolution and sensitivity, and represents the next generation of detection technology.

[0003] However, existing direct detection semiconductor materials face significant challenges. Inorganic semiconductor materials such as zinc cadmium telluride (CdZT) offer excellent performance but suffer from high manufacturing costs, long growth cycles, and environmental toxicity. While organic semiconductor materials offer advantages such as low cost, good flexibility, and solution processing capabilities, most struggle to simultaneously meet the key performance requirements for direct detection, including high resistivity, high carrier mobility-lifetime product, and excellent long-term stability.

[0004] Ethyl p-hydroxybenzoate (EHB), as a known organic compound, is currently prepared primarily using melt methods. This method easily introduces thermal stress and lattice defects during crystallization, severely affecting the material's electrical properties and uniformity, resulting in its carrier transport performance failing to meet the stringent requirements of high-performance direct X-ray detection. While solution methods avoid thermal stress, their long growth cycle and difficulty in controlling nucleation lead to limited crystal size, inconsistent quality (e.g., with solvent inclusions), and poor reproducibility, similarly failing to meet the demands of device applications for large-area, high-integrity crystals.

[0005] Currently, there are no publicly reported processes for preparing high-quality ethyl p-hydroxybenzoate organic semiconductor crystals using solution methods, nor are there any related technologies for applying them to the field of direct X-ray detection. Therefore, developing a solution method that can stably prepare high-quality ethyl p-hydroxybenzoate crystals and verifying its excellent performance in direct X-ray detection has significant technological innovation value and practical application significance. Summary of the Invention

[0006] To address the shortcomings of the aforementioned background technologies, this invention provides a solution-based preparation method for ethyl p-hydroxybenzoate single crystals and its application in X-ray detection. This method achieves, for the first time, the solution-based preparation of large-size ethyl p-hydroxybenzoate crystals and applies it to direct X-ray detection, providing a new technical solution to address the problems of high cost and complex preparation of traditional detection materials.

[0007] The first objective of this invention is to provide a solution-based method for preparing ethyl paraben single crystals, comprising the following steps: Ethyl paraben powder was dissolved in acetone, and then petroleum ether was added to form a mixed solution. The solution was then evaporated to obtain seed crystals. Ethyl p-hydroxybenzoate powder was uniformly dispersed in acetone to obtain an acetone solution; Seed crystals were placed in an acetone solution and then placed in a sealed container. Crystal growth was carried out at 0-5 °C to obtain large-sized crystals. Large-sized crystals are cut along crystal cleavage planes to obtain ethyl p-hydroxybenzoate single crystals with flat surfaces.

[0008] Preferably, the ethyl paraben powder is obtained according to the following steps: The ethyl p-hydroxybenzoate raw material was purified 2-3 times to obtain ethyl p-hydroxybenzoate powder. Each purification process included: dissolving the ethyl p-hydroxybenzoate raw material in acetone, filtering it using an organic filter membrane with a pore size of 0.22 μm, and then recrystallizing it at room temperature.

[0009] Preferably, during crystal growth, the seed crystal is fixed on the surface of a glass slide, acetone solution is injected, the container is sealed with a sealing film, and then placed in an ice-water mixture at 0~5 ℃ for 24~48 hours to grow. The concentration of the acetone solution is 0.27~0.29 g / ml.

[0010] Preferably, when preparing the seed crystals, the ratio of the amount of ethyl paraben powder to acetone and petroleum ether is: (1.8~2.5 g): (10~15 mL): (2-3 mL). When the solution evaporates, it is allowed to stand at room temperature for 36 to 48 hours.

[0011] Preferably, the large-sized crystal is cut along the cleavage plane of the crystal (202).

[0012] The second objective of this invention is to provide a single crystal of ethyl p-hydroxybenzoate.

[0013] Preferably, the hole mobility of the single crystal is not less than 14.0 cm⁻¹. 2 V -1 s -1Hole mobility-lifetime product not less than 1.0 × 10 -4 cm 2 V -1 .

[0014] The third objective of this invention is to provide an application of ethyl p-hydroxybenzoate single crystals in direct X-ray detection or direct X-ray imaging.

[0015] Preferably, when ethyl paraben single crystals are used in direct X-ray detection, the transmittance of ultraviolet-visible-near-infrared light in the wavelength range above 400 nm is not less than 75%.

[0016] The fourth objective of this invention is to provide a direct X-ray detector that uses ethyl p-hydroxybenzoate single crystal as the detection material.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a solution-based method for the preparation of ethyl p-hydroxybenzoate single crystals and its application in X-ray detection. This method successfully overcomes the inherent defects of traditional melt methods in crystal growth, yielding ethyl p-hydroxybenzoate (C9H) with excellent crystal quality and photoelectric properties. 10 O3 (EHB) organic crystal. This crystal material exhibits comprehensive properties suitable for direct X-ray detection. Detectors made based on it show significant advantages in sensitivity, response speed, and stability, breaking through the performance limitations of existing organic semiconductor materials in the field of X-ray detection and providing a reliable material basis and technical solution for the development of new X-ray imaging systems. Attached Figure Description

[0018] Figure 1 This describes the crystal growth and wafer fabrication process for EHB crystals.

[0019] Figure 2 EHB crystals prepared under different preparation conditions. (a) Crystals grown from unpurified raw materials; (b) Crystals grown from low-concentration solutions; (c) Crystals grown from high-concentration solutions; (d) Crystals grown from a mixed solution of acetone and petroleum ether; (e) Large-sized single crystals grown by the seed crystal method; (f) Wafers cut along the (202) crystal plane; (g) Crystals volatilized at room temperature with 4.2 g purified raw materials / 15 mL acetone (without petroleum ether); (h) Crystals volatilized at 0 °C with 4.2 g purified raw materials / 15 mL acetone (without petroleum ether); (i) Crystals grown at 0 °C with 8.5 g purified raw materials / 30 mL acetone (without seed crystal).

[0020] Figure 3 Structural characterization of the prepared EHB crystal. (a) Molecular stacking structure; (b) X-ray diffraction pattern.

[0021] Figure 4 Optical properties of EHB crystal. (a) Ultraviolet-visible-near-infrared transmission spectrum; (b) Tauc plot bandgap calculation.

[0022] Figure 5 The electrical transport properties of the EHB crystal are shown in the following figures: (a) Schematic diagram of the coplanar detector structure; (b) Signal fall time under different bias voltages; (c) Hole drift time distribution; (d) Hole mobility fitting; (e) Alpha particle energy spectrum; (f) Mobility-lifetime product fitting; (g) Alpha energy spectrum stability test.

[0023] Figure 6 X-ray detection performance of EHB crystal. (a) X-ray absorption cross section; (b) IV characteristic curve; (c) time response characteristics; (d) current-time response; (e) on / off ratio and bias voltage relationship; (f) sensitivity fitting; (g) sensitivity voltage dependence; (h) low-dose real-time response; (i) derivation of detection limit.

[0024] Figure 7 X-ray imaging performance of EHB crystal. (a) Long-term stability test; (b) Line-to-card resolution test; (c) Edge spread function; (d) Modulation transfer function; (e) Imaging of capsule internal structure; (f) Pen tip structure imaging; (g) Chip imaging at different dose rates. Detailed Implementation

[0025] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0026] This invention aims to provide a solution-based preparation method for ethyl paraben single crystals and its application in X-ray detection. The method includes: dissolving purified raw materials in acetone, adding petroleum ether to form a mixed solution, and obtaining a seed crystal through solution evaporation; preparing a near-saturated acetone solution, placing the seed crystal in a sealed container, and growing the crystal at low temperature to obtain a large-size single crystal; finally, cutting along the crystal cleavage plane to obtain a wafer for device fabrication. This invention is the first to achieve a solution-based preparation method for large-size ethyl paraben crystals and apply it to direct X-ray detection, providing a new technical solution to solve the problems of high cost and complex preparation of traditional detection materials.

[0027] To achieve the above objectives, the first aspect of the present invention provides a solution-based method for preparing ethyl p-hydroxybenzoate single crystals, comprising the following steps: Ethyl paraben powder was dissolved in acetone, and then petroleum ether was added to form a mixed solution. The solution was then evaporated to obtain seed crystals. Ethyl p-hydroxybenzoate powder was uniformly dispersed in acetone to obtain an acetone solution; Seed crystals were placed in an acetone solution and then placed in a sealed container. Crystal growth was carried out at 0-5 °C to obtain large-sized crystals. Large-sized crystals were cut along the (202) cleavage plane of the crystal to obtain ethyl p-hydroxybenzoate single crystals with flat surfaces.

[0028] In this invention, the preparation mechanism of ethyl p-hydroxybenzoate single crystals is as follows: through the polar synergistic effect of the acetone-petroleum ether mixed solvent, the thermodynamic state of the solution is precisely controlled to the metastable supersaturated region, which avoids insufficient driving force and suppresses the nucleation of impurity crystals, providing continuous and moderate growth conditions for the crystal; based on this, a structurally complete seed crystal is introduced as an orientation template to reduce the homogeneous nucleation energy barrier and guide solute molecules to assemble in an orderly manner along the seed crystal lattice through hydrogen bonds and van der Waals forces; combined with a low-temperature static process, thermal disturbance defects are suppressed and molecular diffusion is slowed down, promoting the slow growth of the crystal in a near-equilibrium state, ultimately obtaining a large-size, highly intact single crystal; subsequently, mechanical separation is performed along its inherent cleavage plane to maintain lattice integrity and anisotropy, thereby obtaining a semiconductor wafer suitable for the requirements of high-performance devices.

[0029] The solution evaporates due to the evaporation of acetone and petroleum ether, and the solution gradually becomes supersaturated, causing crystals to precipitate.

[0030] The ethyl p-hydroxybenzoate powder is obtained by the following steps: the ethyl p-hydroxybenzoate raw material is purified repeatedly 2 to 3 times, each purification including: dissolving it in acetone, filtering it with organic filter paper with a pore size of 0.22 μm, and then recrystallizing it at room temperature.

[0031] The seed crystal is prepared by dissolving 1.8-2.5 g of purified ethyl p-hydroxybenzoate powder in 10-15 mL of acetone, adding 2-3 mL of petroleum ether to form a mixed solution, and allowing it to stand at room temperature (20-25 °C) for 36-48 hours to volatilize, thereby obtaining the seed crystal.

[0032] The method for growing large-size single crystals is as follows: a seed crystal is fixed on the surface of a glass slide placed at the bottom of a beaker, and a nearly saturated acetone solution with a concentration of 0.27~0.29 g / mL is injected into the beaker. After sealing the container, it is placed in an ice-water mixture and grown under constant temperature conditions for 24~48 hours. This concentration condition controls the system in the metastable supersaturated region, with the supersaturation degree between the growth driving force threshold and the homogeneous nucleation critical value. This can suppress spontaneous nucleation while providing a directional growth driving force for the seed crystal, achieving epitaxial ordered deposition, and ultimately achieving the controllable preparation of large-size, highly intact, single-orientation single crystals.

[0033] The near-saturated acetone solution with a concentration of 0.27~0.29 g / mL was obtained by uniformly dispersing ethyl p-hydroxybenzoate powder in acetone.

[0034] It should be noted that seed crystal growth in a near-saturated acetone solution involves precisely controlling the system within a metastable supersaturated region. The supersaturation level is between the growth driving force threshold and the homogeneous nucleation critical value, thus suppressing spontaneous nucleation in the solution while providing a dedicated growth driving force for the seed crystal. Before growth, the seed crystal undergoes a brief, controllable, slight re-dissolution, selectively dissolving to eliminate surface defects such as mechanical damage and adsorbed impurities, obtaining a stable interface. Using this interface as a template, solute molecules undergo epitaxial, ordered deposition along the seed crystal under controlled mass transfer kinetics, ultimately achieving the controllable preparation of large-size, highly intact, single-orientation single crystals.

[0035] The wafer is prepared by using a blade to precisely cut along the natural cleavage plane (202) of the crystal to obtain a wafer with uniform thickness and a large area of ​​exposed cleavage plane.

[0036] A second aspect of the present invention provides an ethyl paraben single crystal, wherein the hole mobility of the single crystal is not less than 14.0 cm⁻¹. 2 V -1 s -1 Hole mobility-lifetime product not less than 1.0 × 10 -4 cm 2 V -1 .

[0037] The molecular formula of ethyl p-hydroxybenzoate single crystal is C9H 10 O3. The structural formula is: .

[0038] A third aspect of the present invention provides the application of ethyl p-hydroxybenzoate single crystal in direct X-ray detection or direct X-ray imaging.

[0039] When used for direct X-ray detection, the single crystal needs to be directionally cut along its (202) crystal plane. This cleavage plane is a natural fracture plane dominated by weak intermolecular bonding in the crystal. The molecules in the plane form highly ordered continuous charge transport channels through OH···O hydrogen bonds and π-π stacking, which can provide a directional and efficient migration path for the charge carriers generated by X-ray excitation. At the same time, cutting along the intrinsic cleavage plane can maintain the integrity of the crystal structure and the continuity of molecular orbitals to the greatest extent, avoiding surface lattice distortion and transport path breakage caused by random cutting, thereby giving full play to the intrinsic advantages of the crystal's high charge carrier mobility and low defect density, and meeting the core requirements of direct X-ray detectors for high sensitivity, low noise and high stability.

[0040] When ethyl p-hydroxybenzoate single crystals are used in direct X-ray detection, the transmittance of ultraviolet-visible-near-infrared light in the wavelength range above 400 nm is not less than 75%.

[0041] It should be noted that cutting the crystal along the (202) cleavage plane is crucial in utilizing this cleavage plane as a naturally exposed interface dominated by weak intermolecular interactions. The in-plane molecular arrangement strictly follows the symmetry of the space group P21 / c, forming a continuous chain structure through OH…O hydrogen bonds accompanied by regular π-π stacking, thus constructing a directional and ordered efficient charge transport channel. At the same time, it avoids the destruction of molecular arrangement by artificial cutting and preserves the continuity of in-plane molecular orbital overlap to the greatest extent. In contrast, the surface of an uncut crystal is a randomly oriented irregular interface, with impaired molecular arrangement, broken transport paths formed by hydrogen bond chains and π-π stacking, and disordered molecular orientation. This not only fails to provide a smooth directional migration channel for X-ray excited charge carriers, but the surface is also prone to defects due to lattice distortion, further hindering charge carrier transport. This directional cutting allows the crystal to precisely match the core requirements of direct X-ray detection for efficient charge carrier collection, low noise, and high stability based on the intrinsic advantages of ordered molecular arrangement (high charge carrier mobility, low defect density, and uniform properties).

[0042] A fourth aspect of the present invention provides a direct X-ray detector that uses ethyl p-hydroxybenzoate single crystal as the detection material.

[0043] It should be noted that, unless otherwise specified, the experimental methods used in this invention are all conventional methods; and the reagents and materials used, unless otherwise specified, are all commercially available.

[0044] The raw materials and reagents used in this embodiment are as follows: ethyl p-hydroxybenzoate organic semiconductor powder (C9H... 10 O3 (AR≥99%) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; petroleum ether (C6H) was also purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. 14 The acetone (C3H6O, AR≥99.0%) was purchased from Tianjin Kemei Chemical Reagent Co., Ltd.; the acetone (C3H6O, AR≥99.7%) was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0045] This embodiment uses the following instruments and testing methods to complete material characterization and performance testing: Material structure characterization: The crystal structure was tested using a Bruker D8 QUEST X-ray diffractometer (Germany); the optical transmittance was characterized using a Shimadzu UV-3150 UV-Vis-NIR spectrophotometer (Japan).

[0046] Device electrode fabrication: Gold electrodes were deposited on the crystal surface using a vacuum evaporation method with an Auto 306 vacuum deposition system from HHV Ltd., UK.

[0047] Electrical performance testing: Carrier transport performance was tested using the alpha particle energy dispersive spectroscopy method. 241 Alpha particles are generated by an Am radioactive source. A test system consisting of an Imdetek MA-01A preamplifier, an ORTEC 673 shaping amplifier, and an Imdetek AMCA-01 multichannel analyzer is used to measure the flight time, carrier mobility, and mobility-lifetime product of the crystal detector.

[0048] X-ray detection performance evaluation: A LIOTIMES LUX-50-50PC1-D beryllium window microfocus X-ray source was used in conjunction with a Radcal T3 Accu-Dose+ Pro dosimeter for dose rate calibration. A Keithley 6517B electrometer was used to record photocurrent data. The system evaluated key performance parameters such as the detector's sensitivity, detection limit, and stability.

[0049] Imaging performance test: Based on the ZYY-DZSZXT-100 imaging platform of Beijing Zhenyaoyan Technology Co., Ltd., and combined with the Keithley 6517B electrometer to record the transmitted X-ray photocurrent data, spatial resolution imaging results were obtained through data processing.

[0050] Example 1 See Figure 1 As shown, a method for preparing ethyl p-hydroxybenzoate single crystals includes the following steps: Seed crystal preparation: First, the raw material was purified: 30.0 g of ethyl p-hydroxybenzoate powder (AR≥99.0%) was weighed and dissolved in 150 mL of acetone (AR≥99.7%) by stirring. After filtration through a 0.22 μm nylon filter membrane, the filtrate was allowed to stand for 36 hours to allow the solvent to evaporate naturally, yielding the recrystallized product. This purification process was repeated three times to ensure the purity of the raw material.

[0051] 1.8 g of the purified product was dissolved in 10 mL of acetone, and 2.0 mL of petroleum ether was added to form a mixed solution. The addition of petroleum ether, by adjusting the solvent polarity and evaporation rate, precisely controlled the solution state within the metastable crystallization region, effectively suppressing disordered nucleation. The mixed solution was allowed to stand at room temperature for 36 hours to evaporate, yielding seed crystals with regular morphology. Large-size crystal preparation: 8.5 g of purified ethyl paraben raw material was weighed and placed in a clean, dry beaker. 30 mL of acetone (AR ≥ 99.7%) was added, and a near-saturated solution was prepared by magnetic stirring. An ultrasonically cleaned glass slide was used as the substrate and placed flat at the bottom of another clean beaker. The prepared solution was slowly poured along the wall, avoiding disturbance. A seed crystal with a complete morphology was selected and precisely placed on the surface of the glass slide. The beaker was then completely sealed using a sealing film. The sealed growth system was placed in a 0 ℃ constant temperature device. Utilizing the micro-dissolution-recrystallization equilibrium mechanism occurring on the seed crystal surface, directional epitaxial growth of the solute on the seed crystal template was achieved. After standing for 36 hours, the crystals were removed, yielding large crystals with dimensions in the centimeter range.

[0052] Preparation of ethyl p-hydroxybenzoate wafers: Take the obtained large-size crystal and use a single-edged blade to perform directional cutting along the (202) cleavage plane of the crystal. Keep the blade parallel to the cleavage plane during cutting, and obtain a wafer with a complete surface and uniform thickness by precisely controlling the cutting angle and applying uniform slight pressure, taking advantage of the crystal cleavage properties.

[0053] Example 2 Same as Example 1, except that: In the seed crystal preparation stage, 4.2 g of the purified product described in Example 1 was directly dissolved in 15 mL of acetone (without adding petroleum ether), and the solution was allowed to stand at room temperature for 36 hours to evaporate. The resulting crystals were mostly flat and had obvious step defects on the surface, poor crystal regularity, and poor overall quality.

[0054] Example 3 Same as Example 1, except that: In the seed crystal preparation stage, 4.2 g of the purified product described in Example 1 was directly dissolved in 15 mL of acetone (without adding petroleum ether), and the solution was placed in a 0 ℃ constant temperature device to evaporate for 48 hours. The resulting crystal had severe step defects on the surface, poor crystal surface flatness, obvious liquid phase encapsulation, no clear regular morphology, and poor crystal quality.

[0055] Example 4 Same as Example 1, except that: In the large-size crystal preparation stage, 8.5 g of purified ethyl paraben raw material was weighed and dissolved in 30 mL of acetone to prepare a near-saturated solution. After the solution was poured into a clean beaker, without placing a seed crystal, the beaker was directly sealed with sealing film and placed in a 0 ℃ constant temperature device for 36 hours. Due to the lack of seed crystal for directional guidance, the system exhibited irregular nucleation, and the crystals were mostly in clusters. Not only were there obvious step defects on the surface, but there was also liquid phase encapsulation, resulting in extremely poor crystal quality.

[0056] Comparative Example 1 8.5 g of unpurified ethyl p-hydroxybenzoate raw material was weighed and added to 30 mL of acetone (AR≥99.7%). The mixture was magnetically stirred until completely dissolved. After sealing with sealing film, the mixture was left to grow at room temperature for 24 hours. Due to the large amount of impurities in the raw material, heterogeneous nucleation occurred during the crystal nucleation stage. The resulting crystals were highly aggregated and extremely uneven in size, with obvious white impurity particles adhering to the surface. The overall transparency of the crystals was extremely poor, exhibiting a disordered polycrystalline stacking state and an irregular single-crystal morphology, making it impossible to obtain high-quality crystals suitable for device fabrication.

[0057] Comparative Example 2 1.2 g of ethyl p-hydroxybenzoate (EPR) purified by three recrystallizations was weighed and added to 10 mL of acetone (AR≥99.7%). The mixture was magnetically stirred until completely dissolved to form a low-concentration solution. After sealing with a sealing film, the solution was left to grow at room temperature for 24 hours. Due to the low solution concentration and insufficient supersaturation, the crystal growth driving force was lacking. The resulting crystals were predominantly flat and plate-like, thin, small in size, and sparsely distributed. This failed to meet the minimum size requirements for device fabrication, and the crystal structure was loose and of poor quality, lacking the structural integrity necessary for use as seed crystals.

[0058] Comparative Example 3 3.0 g of ethyl p-hydroxybenzoate raw material, purified by three recrystallizations, was weighed and added to 10 mL of acetone (AR≥99.7%). The mixture was magnetically stirred until completely dissolved to form a high-concentration solution. Due to the excessively high supersaturation of the solution, explosive nucleation occurred during growth, leading to the rapid precipitation of numerous impurity crystals that competed for growth. The resulting crystals were severely aggregated, irregularly shaped, contained obvious liquid-phase inclusions, had rough surfaces with numerous growth steps, and exhibited poor overall quality and insufficient structural integrity, making them unsuitable as seed crystals.

[0059] To illustrate the performance and applications of the ethyl p-hydroxybenzoate (EHB) organic semiconductor crystal prepared according to this invention, the accompanying drawings are provided.

[0060] Figure 1This invention demonstrates the complete process flow for EHB organic semiconductor crystal growth and wafer fabrication. The process comprises three key stages: first, high-quality seed crystals are obtained through raw material dissolution, petroleum ether-controlled crystallization kinetics, and solution evaporation; subsequently, a low-temperature seed crystal method is used for directional epitaxial growth under isothermal conditions to obtain large-size crystals; finally, mechanical cleavage is performed along the (202) cleavage plane of the crystal to obtain semiconductor wafers with intact surfaces. The entire process systematically demonstrates the complete process from raw material purification to device-level wafer fabrication. The seed crystal preparation stage effectively controls crystal nucleation through solvent compatibility; the crystal growth stage utilizes low-temperature conditions to ensure stable epitaxial growth; and the wafer fabrication stage fully leverages the cleavage properties of the crystal, providing an ideal semiconductor material for high-performance X-ray detectors.

[0061] Figure 2 EHB crystals under different preparation conditions are shown, wherein: (a) is a crystal grown from the unpurified raw material provided in Comparative Example 1, with a rough surface and impurities; (b) is a crystal grown from the low-concentration solution provided in Comparative Example 2, with significantly smaller size; (c) is a crystal grown from the high-concentration solution provided in Comparative Example 3, with irregular morphology and multiple crystal nuclei; (d) is a crystal grown from the acetone-petroleum ether mixed solution provided in Example 1, with regular morphology and uniform size; (e) is a large-sized single crystal grown from the seed crystal method provided in Example 1, with a smooth surface and complete crystal shape; (f) is a diced wafer provided in Example 1, with smooth cleavage surfaces and uniform thickness; (g) is a 4.2 g purified raw material / 15 mL acetone (without petroleum ether) room temperature volatilized crystal provided in Example 2, which is flat and has obvious step defects on the surface; (h) is a 4.2 g purified raw material / 15 mL acetone (without petroleum ether) room temperature volatilized crystal provided in Example 3. (i) Crystals grown at 0 °C using 8.5 g purified raw material / 30 mL acetone (without seed crystal) showed severe surface step defects, liquid phase encapsulation, and poor crystal surface flatness. Crystals grown at 0 °C using 8.5 g purified raw material / 30 mL acetone (without seed crystal) from Example 4 exhibited irregular clusters with liquid phase encapsulation. The results indicate that the purity of the raw material, solution concentration, and growth process collectively determine the final quality of the crystals. The mixed solution control and seed crystal growth method employed in this invention can effectively obtain high-quality crystals. In contrast, Examples 2-4, lacking mixed solution polarity control or seed crystal orientation guidance, exhibited problems such as cluster aggregation, surface defects, and liquid phase encapsulation, resulting in significantly lower quality than the product of Example 1. This further verifies the crucial role of the process in improving crystal quality.

[0062] Figure 3The following X-ray diffraction patterns are shown: (a) the crystal stacking structure of the EHB molecule provided in Example 1, and (b) the X-ray diffraction pattern of the main exposed crystal faces after cutting. XRD results show that the crystal exhibits a preferred orientation along the (202) crystal face. On the (202) crystal face, the molecules form a two-dimensional network structure through OH···O hydrogen bonds (bond length approximately 2.94 Å), while the π-π stacking between benzene rings and the van der Waals forces of the alkyl chains further enhance the stability of the crystal face. This ordered molecular arrangement and strong interactions provide an ideal channel for carrier transport, contributing to improved X-ray detector performance.

[0063] Figure 4 The results of the ultraviolet-visible-near-infrared spectral characterization of the crystal provided in Example 1 are as follows: (a) The transmittance of the crystal is as high as 75% in the band above 400 nm, indicating that it has excellent optical quality; (b) The band gap of the crystal is calculated to be 4.14 eV by Tauc plot. This wide band gap characteristic is beneficial to reducing the dark current noise of the device.

[0064] Figure 5 The electrical transport properties of the EHB crystal provided in Example 1 were characterized. (a) is a schematic diagram of the device structure. A coplanar detector was prepared by depositing gold electrodes on the (202) crystal plane. The device structure includes: depositing two parallel electrodes on the upper surface of the EHB crystal. The non-conductive surface of the crystal is fixed to the insulating substrate of the printed circuit board (PCB) by a highly insulating adhesive layer to achieve mechanical support and electrical isolation. Subsequently, conductive copper wires from the source (S) and gate (G) were precisely bonded to the corresponding electrode contact points on the upper surface of the EHB crystal using conductive carbon adhesive, completing the electrical interconnection. Its working principle is based on the generation of electron-hole pairs through radiation ionization, which then drift directionally under an external electric field to form a collecting current. (b) The signal fall times under different reverse bias voltages (-200 V to -600 V) are shown as 20.2 μs, 14.8 μs, 11.1 μs, 8.5 μs, and 7.1 μs, respectively. (c) The Gaussian distribution statistics of the average hole drift time under different voltages are presented. (d) The hole mobility was obtained as 14.54 cm⁻¹ through linear fitting. 2 V -1 s -1 (e) The energy spectra of alpha particles under different bias voltages were recorded; (f) The hole mobility-lifetime product was obtained by fitting the data using the Hecht equation and was found to be 1.75 × 10⁻⁶. -4 cm 2 V -1 (g) shows the stability of the α energy spectrum measured every 20 minutes. These results indicate that the EHB crystal possesses excellent carrier transport properties and stability, meeting the requirements of high-performance X-ray detectors.

[0065] Figure 6The X-ray detection performance of the EHB crystal provided in Example 1 was characterized. (a) X-ray single-photon energy absorption cross section of the EHB crystal; (b) IV characteristic curve, with a measured resistivity of 7.2 × 10⁻⁶. 12 Ω cm; (c) at a bias of 50 V and 62.89 μGy s -1 (d) Response characteristics at different dose rates: rise time 62.4 ms, fall time 63.8 ms; (e) Current-time response curves at different voltages and dose rates; (f) On / off ratio versus bias voltage; (g) Sensitivity versus voltage fitting curves; (h) Sensitivity versus voltage variation; (i) Real-time response at low dose rates with a 50 V bias voltage; (d) Detection limit derivation, down to 23.1 nGy s. -1 These results indicate that the EHB crystal possesses comprehensive advantages such as high resistivity, fast response, excellent sensitivity, and extremely low detection limit, meeting the requirements of high-performance direct X-ray detectors.

[0066] Figure 7 The X-ray imaging performance of the EHB crystal provided in Example 1 was characterized. (a) The device ( Figure 5 Long-term stability and cycle stability of the device shown in the image: After eight months, the dark current decreased from 1.15 × 10⁻⁶. -10 nA cm -1 s -1 V -1 Drift to 1.5×10 -10 nA cm -1 s -1 V -1 The photocurrent is 7.35 × 10 -9 nA cm -1 s -1 V -1 Drifted to 8.32×10 -9 nAcm -1 s -1 V -1 (a) The line-pair card imaging display has a spatial resolution of 3.7 lp mm. -1 (c) and (d) The MTF curves calculated based on ESF and LSF show a theoretical resolution of 6.1 lp mm. -1 (e) at 1.1 μGy s -1 Imaging of nickel-wire-containing capsules at dose rates; (f) at 1.1 μGy s -1 Imaging of a ballpoint pen tip at dose rate; (g) at 1.1 μGy s -1 775 nGy s -1 and 303 nGy s -1Chip imaging at dose rate. All imaging results clearly resolved the fine internal structure of the object, demonstrating the detector's excellent imaging performance.

[0067] In summary, the present invention provides a solution-based organic semiconductor crystal of ethyl p-hydroxybenzoate and its application in direct X-ray detection and imaging. Compared with the melt crystal growth process and traditional inorganic detection materials used in some existing technologies, this invention can achieve excellent crystal quality and high hole mobility (14.54 cm⁻¹) through a controllable low-temperature solution process. 2 V -1 s -1 ) and high mobility-lifetime product (1.75×10 -4 cm 2 V -1 Large-sized crystals were used to prepare a product with high sensitivity and low detection limit (307 μC Gy). -1 cm -2 23.1 nGy s -1 Fast response (rise / fall time approximately 63 ms), high spatial resolution (3.7 lp mm) -1 This provides a novel material system and device solution for achieving low-dose, high-resolution X-ray imaging, featuring a direct X-ray detector with excellent stability.

[0068] This invention describes preferred embodiments and their effects. However, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to include both the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0069] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A solution-based method for preparing ethyl p-hydroxybenzoate single crystals, characterized in that, Includes the following steps: Ethyl paraben powder was dissolved in acetone, and then petroleum ether was added to form a mixed solution. The solution was then evaporated to obtain seed crystals. Ethyl p-hydroxybenzoate powder was uniformly dispersed in acetone to obtain an acetone solution; Seed crystals were placed in an acetone solution and then placed in a sealed container. Crystal growth was carried out at 0-5 °C to obtain large-sized crystals. Large-sized crystals are cut along crystal cleavage planes to obtain ethyl p-hydroxybenzoate single crystals with flat surfaces.

2. The solution method for preparing ethyl p-hydroxybenzoate single crystals according to claim 1, characterized in that, The ethyl p-hydroxybenzoate powder is obtained according to the following steps: The ethyl p-hydroxybenzoate raw material was purified 2-3 times to obtain ethyl p-hydroxybenzoate powder. Each purification process included: dissolving the ethyl p-hydroxybenzoate raw material in acetone, filtering it using an organic filter membrane with a pore size of 0.22 μm, and then recrystallizing it at room temperature.

3. The solution method for preparing ethyl p-hydroxybenzoate single crystals according to claim 1, characterized in that, During crystal growth, the seed crystal is fixed on the surface of a glass slide, acetone solution is injected, the container is sealed with sealing film, and then placed in an ice-water mixture at 0~5 ℃ for 24~48 hours to grow. The concentration of the acetone solution is 0.27~0.29 g / ml.

4. The solution method for preparing ethyl p-hydroxybenzoate single crystals according to claim 1, characterized in that, When preparing seed crystals, the ratio of ethyl paraben powder to acetone and petroleum ether is: (1.8~2.5 g): (10~15 mL): (2-3 mL). When the solution evaporates, it is allowed to stand at room temperature for 36 to 48 hours.

5. The solution method for preparing ethyl p-hydroxybenzoate single crystals according to claim 1, characterized in that, The large crystal was cut along the (202) cleavage plane of the crystal.

6. A single crystal of ethyl p-hydroxybenzoate prepared by the method according to any one of claims 1 to 5.

7. The ethyl p-hydroxybenzoate single crystal according to claim 6, characterized in that, The hole mobility of this single crystal is no less than 14.0 cm⁻¹. 2 V -1 s -1 Hole mobility-lifetime product not less than 1.0 × 10 -4 cm 2 V -1 .

8. The application of the ethyl p-hydroxybenzoate single crystal according to claim 6 in direct X-ray detection or direct X-ray imaging.

9. The application according to claim 8, characterized in that, When ethyl p-hydroxybenzoate single crystals are used in direct X-ray detection, the transmittance of ultraviolet-visible-near-infrared light in the wavelength range above 400 nm is not less than 75%.

10. A direct-type X-ray detector, characterized in that, The direct X-ray detector uses ethyl p-hydroxybenzoate single crystal as described in claim 6 as the detection material.

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