A method for laser-induced fabrication of micro- and nano-structured organic single crystals

Abstract

This invention discloses a laser-induced method for preparing micro / nano-structured organic single crystals, belonging to the field of organic semiconductor single crystal preparation technology. The method includes the following steps: preparing a Bragg grating on a clean, dry glass substrate, and preparing a photothermal thin film on the grating structure; placing the prepared substrate on a processing platform, then adding an organic semiconductor solution to the substrate, and observing the focused position using a CCD camera to ensure it is above the substrate; subsequently, scanning point-by-point with a laser according to a pre-designed program; finally, rinsing with anhydrous ethanol and air-drying. This invention employs the aforementioned laser-induced method for preparing micro / nano-structured organic single crystals, utilizing femtosecond laser irradiation of the grating structure substrate to drive the site-specific aggregation of organic molecules, inducing nucleation and crystallization. By controlling the laser parameters and the grating substrate parameters, in-situ site-specific growth and controllable preparation of micro / nano-structured organic single crystals can be achieved.

Description

Technical Field

[0001] This invention relates to the field of organic semiconductor single crystal preparation technology, and in particular to a method for laser-induced preparation of micro- and nano-structured organic single crystals. Background Technology

[0002] Organic single crystals are crystals with a single lattice structure formed in three-dimensional space by organic molecules through weak intermolecular forces such as van der Waals forces, π-π stacking, and hydrogen bonds. These structures possess long-range order, are free of grain boundaries, and have low defect density. Their molecular orientation, interlayer spacing, and stacking mode directly determine the intrinsic electrical and optical properties of the material. Because single crystals lack the grain boundary scattering and defect traps commonly found in polycrystalline materials, they are often considered ideal model systems for studying the intrinsic properties of organic semiconductors. They are also important material platforms for high-performance organic field-effect transistors, photodetectors, and microlasers.

[0003] However, while many organic single crystals possess light-guiding and light-emitting capabilities, the ordered arrangement of molecules often creates optical waveguide modes within the single crystal, resulting in poor surface emission properties. Therefore, grating-structured treatment of the single crystal surface is commonly used to reduce the influence of waveguide modes and effectively improve external light extraction efficiency. Furthermore, by designing microstructures, the emission angle, polarization, and spectral shape of light can be controlled as needed. However, current methods for structuring organic single crystal surfaces have many shortcomings, making it difficult to simultaneously meet the requirements of rapid growth, programmable positioning, and preservation of single crystal surface properties. This leads to low fabrication efficiency, poor structural controllability, and susceptibility to surface damage, affecting electrical and optical properties. This severely limits the industrial application of micro / nano-structured organic single crystals in high-end optoelectronic devices. Summary of the Invention

[0004] The purpose of this invention is to provide a method for laser-induced preparation of micro / nano-structured organic single crystals. By introducing a photothermal substrate with a Bragg grating structure and combining it with femtosecond laser-induced thermal gradient-driven site-specific nucleation and crystallization of organic molecules, in-situ and controllable growth of micro / nano structures on the surface of organic single crystals can be achieved.

[0005] To achieve the above objectives, this invention provides a method for laser-induced preparation of micro / nano-structured organic single crystals, comprising the following steps: S1. Fabricate a Bragg grating structure on a clean glass substrate; S2. A thin metal film is deposited on the surface of the grating structure to form a photothermal substrate; S3. An organic semiconductor solution is dropped onto a photothermal substrate, and organic molecules are induced to aggregate and crystallize by scanning point by point with a femtosecond laser; S4. Organic single crystals with micro / nano-structured surfaces were obtained by PDMS transfer printing.

[0006] Preferably, in step S1, the Bragg grating structure is prepared by spin-coating diluted NOA63 photoresist onto a glass substrate using a spin coater, followed by helium-neon laser double interference irradiation, development, and drying.

[0007] Preferably, the spin coater has a rotation speed of 6000 rpm, a spin coating time of 20 s, and an acceleration of 1000 rpm / s.

[0008] Preferably, the solvent used for diluting the NOA63 photoresist is acetone, and the concentration of the NOA63 photoresist after dilution is 0.025 g / ml.

[0009] Preferably, the helium-neon laser double interference irradiation time is 12s, the developing solution is acetone, and the developing time is 3s.

[0010] Preferably, in step S2, the deposited metal film is a silver film with a thickness of 10 nm, and the deposition vacuum degree is less than 5 × 10⁻⁶. - 4 Pa.

[0011] Preferably, in step S3, the concentration of the organic semiconductor solution is 0.25-0.35 mg / mL.

[0012] Preferably, in step S3, the solute of the organic semiconductor solution is 2,6-diphenylanthracene, and the solvent is dimethyl sulfoxide.

[0013] Preferably, in step S3, the femtosecond laser has a wavelength of 800nm, a pulse frequency of 80MHz, a pulse width of 120fs, a power of 15-30mW, and a single-point exposure time of 10-500ms.

[0014] Preferably, in step S4, PDMS transfer is achieved by lightly pressing and peeling off the micro / nano structure organic single crystal.

[0015] This invention introduces a photothermal substrate with a Bragg grating structure. When a femtosecond laser irradiates the photothermal thin film substrate with the Bragg grating, the metallic silver film converts the laser energy into heat energy, generating a local thermal gradient and simultaneously forming cavitation bubbles. The thermal gradient and cavitation bubbles together act as a driving force to generate solution convection, driving organic semiconductor molecules to aggregate at the laser scanning site, thereby inducing the nucleation and crystallization of organic molecules. Ultimately, a micro-nano grating structure matching the grating period of the substrate is formed on the surface of the organic single crystal, realizing the micro-nano structuring of the organic single crystal.

[0016] Therefore, the laser-induced method for preparing micro / nano-structured organic single crystals provided by this invention has the following beneficial effects: (1) This invention utilizes the precise controllability of femtosecond lasers to drive organic molecules to aggregate and crystallize at designated sites on the substrate, thereby achieving in-situ fixed-point growth of organic single crystals. Furthermore, the laser-induced crystallization process is a mild solution phase growth process that does not cause physical damage to the surface of the organic single crystal, thus ensuring the intrinsic electrical and optical properties of the single crystal.

[0017] (2) The laser-induced crystallization process of the present invention is a rapid nucleation growth process. A single micro-nano structured organic crystal can complete in-situ growth within 1 minute, which is far more efficient than the existing preparation methods and is suitable for large-scale preparation.

[0018] (3) By adjusting the position of the glass substrate in the interference lithography, substrates with different grating periods (500nm, 700nm, 1μm, 1.5μm) can be prepared, thereby inducing the growth of organic single crystals with different micro-nano structures. The micro-nano grating structure on the surface of the organic single crystal is precisely matched with the Bragg grating period of the substrate, which can effectively improve the light extraction efficiency and can be directly applied to optoelectronic devices such as organic light-emitting diodes and organic lasers.

[0019] (4) The preparation process of this invention is simple and has good repeatability. The micro-nano structure morphology of organic single crystal can be controlled by adjusting parameters such as laser power, single-point exposure time, and scanning spacing to meet the application requirements of optoelectronic devices.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the method for preparing micro / nano-structured organic single crystals induced by femtosecond laser according to the present invention; Figure 2 These are schematic diagrams and corresponding scanning electron microscope (SEM) and atomic force microscope (AFM) images of two growth methods for organic single crystal surface structuring with a grating period of 1 μm in this invention. Wherein, a is an AFM image of a substrate with a grating period of 1 μm; b is a schematic diagram of organic single crystal growing obliquely along the grating stripes; c is a schematic diagram of organic single crystal growing obliquely across the grating stripes; d is a SEM image of an organic single crystal grown on a grating structure using the growth method in c; e is an AFM image of an organic single crystal grown on a grating structure using the growth method in c; f is a three-dimensional AFM image of an organic single crystal grown on a grating structure using the growth method in c; g is a SEM image of an organic single crystal grown on a grating structure using the growth method in b; h is an AFM image of an organic single crystal grown on a grating structure using the growth method in b; and i is a three-dimensional AFM image of an organic single crystal grown on a grating structure using the growth method in b. Figure 3These are optical microscope and atomic force microscope images of the organic single crystal with a grating period of 500 nm in Embodiment 1 of the present invention; wherein a is an atomic force microscope image of the 500 nm grating substrate, b is a depth image of the white line section in a, c is an optical microscope image of the micro-nano structured single crystal with a grating period of 500 nm on the surface, d is an atomic force microscope image of the micro-nano structured single crystal with a grating period of 500 nm on the surface, e is a depth image of the white line section in d, and f is a three-dimensional atomic force microscope image of the micro-nano structured single crystal with a grating period of 500 nm on the surface. Figure 4 These are optical microscope and atomic force microscope images of the organic single crystal with a grating period of 700 nm in Embodiment 2 of the present invention; wherein a is an atomic force microscope image of the 700 nm grating substrate, b is a depth image of the white line section in a, c is an optical microscope image of the micro-nano structured single crystal with a 700 nm grating period on the surface, d is an atomic force microscope image of the micro-nano structured single crystal with a 700 nm grating period on the surface, e is a depth image of the white line section in d, and f is a three-dimensional atomic force microscope image of the micro-nano structured single crystal with a 700 nm grating period on the surface. Figure 5 These are optical microscope and atomic force microscope images of the organic single crystal with a grating period of 1.5 μm in Embodiment 4 of the present invention; wherein a is an atomic force microscope image of the 1.5 μm grating substrate, b is a depth image of the white line section in a, c is an optical microscope image of the micro-nano structured single crystal with a grating period of 1.5 μm on the surface, d is an atomic force microscope image of the micro-nano structured single crystal with a grating period of 1.5 μm on the surface, e is a depth image of the white line section in d, and f is a three-dimensional atomic force microscope image of the micro-nano structured single crystal with a grating period of 1.5 μm on the surface. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims and are all within the protection scope of the present invention.

[0023] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0024] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0025] Unless otherwise specified, the reagents, instruments, and equipment used in this invention are all commonly used by those skilled in the art, and the testing standards all use national or international standards commonly used in the field, without further explanation.

[0026] The following examples use a cover glass sheet with a size of 50×24mm and a thickness of 0.13-0.15mm as a glass substrate.

[0027] Example 1 This embodiment provides a method for laser-induced fabrication of micro / nano-structured organic single crystals with a grating period of 500 nm, as illustrated in the flowchart below. Figure 1 As shown, the specific steps include: S1. Preparation of Bragg grating substrate: A clean and dry coverslip with dimensions of 50×24×0.13mm was selected and placed on a spin coater; NOA63 photoresist was diluted with acetone at a ratio of 1g:40ml (concentration 0.025g / ml), and spin-coated for 20s at a speed of 6000rpm and an acceleration of 1000rpm / s to form a uniform photoresist layer on the surface of the coverslip; the substrate was placed in the double-beam interference path of a helium-neon laser, and the position of the substrate was adjusted so that the grating period was 500nm, and interference irradiation was performed for 12 seconds; then it was developed with acetone for 3 seconds and dried with nitrogen to obtain a Bragg grating substrate with a grating period of 500nm.

[0028] S2. Preparation of the photothermal thin film substrate: The cover glass of the Bragg grating substrate was attached to the mask of the vacuum evaporator using 3M tape. The vacuum pump was started to evacuate the vacuum. When the vacuum level in the cavity reached 5×10⁻⁶, the vacuum was evacuated. -4 At Pa, a silver film was deposited at a rate of 1 Å / s. The film thickness and deposition rate of the deposited material were monitored using a quartz crystal oscillator in the system. The substrate was kept rotating at a constant speed during the deposition process. The deposition was stopped when the silver film thickness was 10 nm, resulting in a photothermal thin film substrate with a Bragg grating.

[0029] S3. Femtosecond Laser Induction: 2,6-Diphenylanthracene (DPA) is a typical small-molecule organic semiconductor with an anthracene-centered conjugated backbone and phenyl substitutions at the 2 and 6 positions. A 0.3 mg / mL DPA solution was prepared using DPA as the organic semiconductor and dimethyl sulfoxide (DMSO) as the solvent. A photothermal thin film substrate with a Bragg grating was placed on a femtosecond laser processing platform, and 5 μL of the above DPA solution was added. The femtosecond laser was focused above the substrate using a CCD camera with a 60x objective lens and a numerical aperture of 1.4. The femtosecond laser parameters were set as follows: wavelength 800 nm, pulse frequency 80 MHz, pulse width 120 fs, power 17 mW, single-point exposure time 100 ms, and scanning interval 20 μm. The scanning trajectory designed in 3Dmax software was exported as a TXT file and then imported into the control computer of the laser direct-writing system. The laser scanned point by point. After scanning, the substrate was rinsed three times with anhydrous ethanol and allowed to air dry.

[0030] S4. Transfer of micro- and nano-structured organic single crystals: The cut PDMS sheet is adhered to the laser processing area of ​​the substrate and gently pressed with a finger for 10 seconds to ensure that the PDMS and the single crystal are fully bonded; then the PDMS is slowly peeled off in the horizontal direction to obtain a micro- and nano-structured DPA single crystal with a 500nm grating period on the surface.

[0031] Example 2 This embodiment provides a method for laser-induced fabrication of micro / nano-structured organic single crystals with a grating period of 700 nm. The only difference from Embodiment 1 is that in step S1, the position of the cover glass in the double-beam interference optical path of the helium-neon laser is adjusted to prepare a Bragg grating substrate with a grating period of 700 nm; in step S2, the cavity vacuum degree is 5 × 10⁻⁶. -4 Pa; In step S3, a DPA solution with a concentration of 0.32 mg / mL was prepared, and focusing was performed using an 80x objective lens with a numerical aperture of 1.4. The femtosecond laser power was adjusted to 20 mW, and the single-point exposure time was adjusted to 150 ms. Finally, a micro / nano-structured DPA single crystal with a 700 nm grating period on its surface was obtained, and the single crystal surface structure was intact with a regular grating tilt angle.

[0032] Example 3 This embodiment provides a method for laser-induced fabrication of micro / nano-structured organic single crystals with a grating period of 1 μm. The only difference from Embodiment 1 is that in step S1, the position of the cover glass in the double-beam interference optical path of the helium-neon laser is adjusted to prepare a Bragg grating substrate with a grating period of 1 μm; in step S2, the cavity vacuum degree is 5 × 10⁻⁶. -4Pa; In step S3, a DPA solution with a concentration of 0.32 mg / mL was prepared, the femtosecond laser power was adjusted to 19 mW, and the single-point exposure time was adjusted to 200 ms. Finally, a micro / nano-structured DPA single crystal with a grating period of 1 μm on its surface was obtained, and the single crystal surface structure was complete with a regular grating tilt angle.

[0033] Example 4 This embodiment provides a method for laser-induced fabrication of micro / nano-structured organic single crystals with a grating period of 1.5 μm. The only difference from Embodiment 1 is that in step S1, the position of the cover glass in the double-beam interference optical path of the helium-neon laser is adjusted to prepare a Bragg grating substrate with a grating period of 1.5 μm; in step S2, the cavity vacuum degree is 5 × 10⁻⁶. -4 Pa; In step S3, a DPA solution with a concentration of 0.32 mg / mL was prepared, the femtosecond laser power was adjusted to 18 mW, and the single-point exposure time was adjusted to 100 ms. Finally, a micro-nano structured DPA single crystal with a grating period of 1.5 μm on the surface was obtained, and the single crystal surface structure was complete with a regular grating tilt angle.

[0034] The micro-nano structured organic single crystals prepared in Examples 1-4 above were characterized.

[0035] Depend on Figure 2 As can be seen, the schematic diagram shows the structured growth of organic single crystal surfaces using femtosecond laser technology, and the two growth methods of DPA single crystals with surface structured growth when the grating period is 1μm. Figure 2 df is based on Figure 2 In single crystals grown using the c-growth method, the grating structure on the crystal surface is tilted, and the grating period is also 1 μm. The effect of laser-induced convection on the crystal surface growth structure is also evident. Figure a shows the characterization of the grating structure on the substrate. Figure 2 gi is based on Figure 2 In single crystals grown using this method, the grating structure on the crystal surface is also tilted, and the grating period on the crystal surface is also 1μm. Furthermore, the surface structure of single crystals grown using this method is relatively complete.

[0036] Depend on Figure 3 It is known that the femtosecond laser-induced DPA single crystal surface has a grating structure with a period of 500 nm, which is... Figure 3 a and Figure 3 b indicates the substrate morphology and depth of the grating structure with a period of 500 nm, while Figure 3 c to Figure 3 As can be seen from e, the grating structure on the crystal surface has a good morphology, and the period is also 500nm, with a tilt angle.

[0037] Depend on Figure 4It is known that the femtosecond laser-induced DPA single crystal surface has a grating structure with a period of 700 nm, which is... Figure 4 a and Figure 4 b indicates the morphology and depth of the substrate for the grating structure with a period of 700 nm, while Figure 4 c to Figure 4 As can be seen from e, the grating structure on the crystal surface has a good morphology, and the period is also 700nm, with a tilt angle.

[0038] Depend on Figure 5 It can be seen that the femtosecond laser-induced grown DPA single crystal surface has a grating structure with a period of 1.5 μm, which is... Figure 5 a and Figure 5 b indicates the substrate morphology and depth of the grating structure with a period of 1.5 μm, while Figure 5 c to Figure 5 As can be seen from e, the grating structure on the crystal surface has a good morphology and a period of 1.5 μm, and has a tilt angle.

[0039] In summary, this invention is based on a laser-induced growth method for micro / nano-structured organic single crystal surfaces. It utilizes the grating structure on the surface of organic single crystals that can be rapidly grown in situ using lasers. The grating structure is fabricated on a cover glass slide using NOA63 photoresist lithography with a continuous laser, and a metal thin film is deposited on the grating structure as a photothermal conversion substrate. The thermal gradient and cavitation bubbles generated by femtosecond laser irradiation of the metal substrate serve as driving forces to induce convection-induced site-specific aggregation and nucleation of organic molecules. Thus, after growth, the organic single crystal surface possesses a structure corresponding to the micro / nano-grating structure on the substrate, achieving micro / nano-structured organic single crystal surfaces.

[0040] Therefore, this invention employs the above-mentioned method for growing organic single crystals based on laser-induced micro / nano-structured structures. By adjusting the laser parameters and grating substrate parameters, the surface of the grown organic single crystal is induced to have grating structures with different periods, thus realizing the micro / nano-structured structure of the organic single crystal surface.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for laser-induced preparation of micro / nano-structured organic single crystals, characterized in that, Includes the following steps: S1. Fabricate a Bragg grating structure on a clean glass substrate; S2. A thin metal film is deposited on the surface of the grating structure to form a photothermal substrate; S3. An organic semiconductor solution is dropped onto a photothermal substrate, and organic molecules are induced to aggregate and crystallize by scanning point by point with a femtosecond laser; S4. Organic single crystals with micro / nano-structured surfaces were obtained by PDMS transfer printing.

2. The method for laser-induced preparation of micro / nano-structured organic single crystals according to claim 1, characterized in that, In step S1, the Bragg grating structure is prepared by spin-coating diluted NOA63 photoresist onto a glass substrate using a spin coater, followed by helium-neon laser double interference irradiation, development, and drying.

3. The method for laser-induced preparation of micro / nano-structured organic single crystals according to claim 2, characterized in that: The spin coater has a rotation speed of 6000 rpm, a spin coating time of 20 s, and an acceleration of 1000 rpm / s.

4. The method for laser-induced preparation of micro / nano-structured organic single crystals according to claim 2, characterized in that: The solvent used to dilute NOA63 photoresist was acetone, and the concentration of NOA63 photoresist after dilution was 0.025 g / ml.

5. The method for laser-induced preparation of micro / nano-structured organic single crystals according to claim 2, characterized in that: The helium-neon laser double interference irradiation time was 12s, and the developing solution was acetone with a developing time of 3s.

6. The method for laser-induced preparation of micro / nano-structured organic single crystals according to claim 1, characterized in that: In step S2, the deposited metal film is a silver film with a thickness of 10 nm, and the deposition vacuum degree is less than 5 × 10⁻⁶. -4 Pa.

7. The method for laser-induced preparation of micro / nano-structured organic single crystals according to claim 1, characterized in that: In step S3, the concentration of the organic semiconductor solution is 0.25-0.35 mg / mL.

8. The method for laser-induced preparation of micro / nano-structured organic single crystals according to claim 1, characterized in that: In step S3, the solute of the organic semiconductor solution is 2,6-diphenylanthracene, and the solvent is dimethyl sulfoxide.

9. The method for laser-induced preparation of micro / nano-structured organic single crystals according to claim 1, characterized in that: In step S3, the femtosecond laser has a wavelength of 800nm, a pulse frequency of 80MHz, a pulse width of 120fs, a power of 15-30mW, and a single-point exposure time of 10-500ms.

10. The method for laser-induced preparation of micro / nano-structured organic single crystals according to claim 1, characterized in that: In step S4, PDMS transfer is achieved by gently pressing and peeling off the micro / nano structure organic single crystal.

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