A sub-nanometer two-dimensional heterojunction nanopore preparation method based on HIM pre-pore and STEM closed-loop control

Abstract

The application discloses a sub-nanometer two-dimensional heterojunction nanopore preparation method based on HIM pre-pore and STEM closed-loop control, and belongs to the technical field of micro-nano manufacturing and MEMS. The pore prepared by the application has the characteristics of mu epsilon [0.50, 0.90] nm, sigma <= 0.10 nm, RMS <= 0.30 nm and drift rate <= 0.02 nm.h ‑1 The pore preparation process has high repeatability, smooth and stable edges, and is suitable for DNA sequencing, ion screening and environmental complex pollutant detection.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano manufacturing and microelectromechanical systems (MEMS) technology, and particularly relates to a method for preparing sub-nano two-dimensional heterostructure nanopores based on HIM pre-formed pores and STEM closed-loop control. Background Technology

[0002] With the development of molecular recognition and single-molecule sequencing technologies, nanoporous devices have shown great potential in the fields of biomedical detection, environmental sensing, and molecular sieving.

[0003] Existing solid-state nanopores are mainly based on silicon nitride (Si3N4) or aluminum oxide (Al2O3) film materials, with typical thicknesses of tens of nanometers. The precision of pore size control is limited, and resolution can usually only be achieved at the 2-5 nm level. Such devices suffer from problems such as signal ambiguity, insufficient spatial resolution, and edge charge interference when detecting single ions or single-stranded DNA molecules.

[0004] Two-dimensional materials (graphene, MoS2, h-BN, etc.) have become ideal candidates for preparing ultrathin nanopores due to their single-atom-level thickness, high mechanical strength, and good chemical stability. In particular, heterojunction structures (such as h-BN / graphene and MoS2 / graphene) can simultaneously achieve insulating and conductive properties, effectively reducing interfacial charge noise and enhancing edge stability.

[0005] However, existing techniques for preparing nanopores in two-dimensional materials still have the following prominent problems:

[0006] 1. Limited lower limit of aperture: HIM (helium ion microscopy) or FIB (focused ion beam) plasma beam drilling can achieve an aperture of about 1-2 nm, but cannot stably break through the sub-1 nm region;

[0007] 2. Uncontrollable edge reconstruction: Although TEM (transmission electron microscopy) drilling can reach the atomic level, aperture drift and random edge shrinkage lead to poor repeatability;

[0008] 3. Lack of real-time feedback control: Traditional hole-forming processes rely solely on post-processing observation and cannot achieve dynamic monitoring and adjustment of hole diameter during the processing.

[0009] Therefore, how to construct a pore-forming method that combines sub-nanometer-level pore size control accuracy, real-time closed-loop feedback capability, and statistical reproducibility has become a key problem that needs to be solved in two-dimensional nanopore technology. Summary of the Invention

[0010] To address the aforementioned technical issues, this invention proposes a method for preparing sub-nanometer two-dimensional heterostructure nanopores based on HIM (helium ion microscopy) pre-forming and STEM (scanning transmission electron microscopy) closed-loop control. Through multimodal integration, the method achieves continuous and controllable convergence of pore sizes in the range of 0.5-0.9 nm, possessing Å-level control precision and long-term structural stability.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] This invention provides a method for preparing sub-nanometer two-dimensional heterostructure nanopores based on HIM pre-formed pores and STEM closed-loop control, comprising the following steps:

[0013] (1) Transferring a two-dimensional heterojunction thin film on a windowed Si3N4 chip;

[0014] (2) Using HIM to prepare nanopores with an initial pore size of 1-3 nm on the product obtained in step (1);

[0015] (3) Transfer the product obtained in step (2) into the STEM cavity, acquire the image of the aperture area in real time in HAADF (high angle annular dark field) mode, and adjust the beam density and scanning path through threshold determination and PID adaptive algorithm to make the aperture stabilize and converge to 0.5-0.9 nm.

[0016] (4) The processing will automatically terminate when Δd ≤ 0.02 nm and RMS (surface roughness at the hole edge) ≤ 0.30 nm; where Δd is the difference between the actual hole diameter and the target hole diameter.

[0017] This invention combines ion beam initial pore formation with in-situ atomic-level electron beam control to achieve precise convergence of pore sizes in a two-dimensional heterojunction system within the range of 0.5-0.9 nm, exhibiting high repeatability and Å-level size control. The invention first uses HIM to form initial pores of 1-3 nm on a two-dimensional heterojunction film, and then achieves Å-level convergence of the pore size in STEM through HAADF image intensity threshold monitoring and PID adaptive control, stabilizing it within the 0.5-0.9 nm range. The pores fabricated in this invention have μ∈[0.50,0.90] nm, σ≤0.10 nm, RMS≤0.30 nm, and drift rate≤0.02 nm·h. -1 With these characteristics, the well-forming process is highly repeatable, with smooth and stable edges, making it suitable for DNA sequencing, ion sieving, and detection of complex environmental pollutants.

[0018] Furthermore, the HIM processing parameters are: beam current 2-5 pA, dose 10-50 nC / μm. 2 Dwell time: 0.1-5 ms.

[0019] Furthermore, after being transferred into the STEM cavity, the STEM accelerating voltage is 60-200 kV, and the closed-loop period is ≤100 ms.

[0020] Furthermore, Δd was calibrated using the mapping between HAADF image intensity and aperture via lattice constant and gold nanoclusters, with an aperture error ≤0.05 nm.

[0021] Furthermore, HIM and STEM are connected via a vacuum channel.

[0022] Furthermore, when transferring the material into the STEM cavity in step (3), the transfer time is ≤5 minutes.

[0023] This invention also provides a sub-nanometer two-dimensional heterojunction nanoporous device, prepared according to the above-described method. The sub-nanometer two-dimensional heterojunction nanoporous device has a pore size range of 0.5-0.9 nm, an edge RMS ≤ 0.30 nm, and a drift rate ≤ 0.02 nm·h. -1 .

[0024] This invention also provides the application of the above-mentioned sub-nanometer two-dimensional heterojunction nanopore device in DNA sequencing.

[0025] This invention also provides the application of the above-mentioned sub-nanometer two-dimensional heterojunction nanoporous devices in ion sieving.

[0026] This invention also provides the application of the above-mentioned sub-nanometer two-dimensional heterojunction nanoporous devices in the detection of environmental composite pollutants.

[0027] Compared with the prior art, the present invention has the following advantages and technical effects:

[0028] 1) Sub-nanometer precision control: For the first time, the pore size in a two-dimensional heterojunction system is stably controlled within the range of 0.5-0.9 nm, with an accuracy reaching the Å level;

[0029] 2) Real-time closed-loop feedback mechanism: Through the HAADF image intensity-aperture mapping relationship and PID adaptive algorithm, dynamic aperture adjustment and automatic termination control are realized;

[0030] 3) High edge lattice continuity: In-situ electron beam reconstruction maintains the hexagonal lattice characteristics of the aperture edge, significantly reducing current noise and aperture drift;

[0031] 4) High repeatability and reliability: Statistical results of 30 holes verified the consistency of hole size distribution and long-term structural stability;

[0032] 5) Good process compatibility: This method can be directly integrated into existing HIM and STEM systems without the need for additional hardware.

[0033] 6) Broad application prospects: The obtained sub-nanopores can be used in high-sensitivity analysis scenarios such as DNA sequencing, ion sieving, and detection of environmental complex pollutants (such as metal-ligand complexes), providing a technical basis for novel nanopore sensors. Attached Figure Description

[0034] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0035] Figure 1 A schematic diagram of the closed-loop control system for the sub-nanometer two-dimensional heterostructure nanopore preparation method based on HIM pre-formed pores and STEM closed-loop control, to realize the present invention.

[0036] Figure 2 This is a schematic diagram of the overall process for the preparation of sub-nano two-dimensional heterostructure nanopores based on HIM pre-formed pores and STEM closed-loop control provided in Example 1, wherein 11-NaOH solution, 101-copper foil, 102-graphene, 103-polymethyl methacrylate (PMMA), 104-sapphire, 105-monolayer hexagonal boron nitride (h-BN), and 106-silicon nitride (Si3N4);

[0037] Figure 3 These are optical microscope images of the h-BN / graphene heterojunction thin film before (a) and after (b) transfer in Example 1 of the present invention.

[0038] Figure 4 The image shows the Raman spectrum of the h-BN / graphene heterojunction film in Example 1.

[0039] Figure 5 The selected area electron diffraction (SAED) pattern of the h-BN / graphene heterojunction film in Example 1 is shown.

[0040] Figure 6 Optical microscope images of the h-BN / graphene heterojunction film in Example 4 at different magnifications (60k×, 80k×, 100k×, 120k×);

[0041] Figure 7 The images shown are micrographs of the initial pores of the two-dimensional heterostructure membrane prepared by helium ion microscopy (HIM) in Example 4. (a) is a fitting diagram of the average diameter of the ion beam under different ion doses, and (b) is a TEM image of the nanopore array obtained under different ion doses.

[0042] Figure 8Comparison of HAADF micrographs of the hole region before and after closed-loop control in Example 5: (a) is the initial HIM hole, and (b) is the hole after STEM convergence.

[0043] Figure 9 The following are graphs showing the pore size convergence process and statistical distribution results in Example 5: (a) is the pore size convergence curve over time, and (b) is a statistical graph of 30 pore samples.

[0044] Figure 10 The image shows the ion current detection results of λ-DNA molecules passing through the sub-nanopore of the heterostructure in Example 5. The upper side is the baseline current of 100mV λ-DNA (concentration 10 ng / μL) control, and the lower side is the detection signal of 200mV λ-DNA (concentration 10 ng / μL). Detailed Implementation

[0045] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0046] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0047] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0048] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0049] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0050] Embodiments of the present invention provide a method for preparing sub-nanometer two-dimensional heterostructure nanopores based on HIM (helium ion microscopy) pre-forming and STEM (scanning transmission electron microscopy) closed-loop control, comprising the following steps:

[0051] (1) Transferring a two-dimensional heterojunction thin film on a windowed Si3N4 chip;

[0052] (2) Using HIM to prepare nanopores with an initial pore size of 1-3 nm on the product obtained in step (1);

[0053] (3) Transfer the product obtained in step (2) into the STEM cavity, acquire the image of the aperture area in real time in HAADF (high angle annular dark field) mode, and adjust the beam density and scanning path through threshold determination and PID adaptive algorithm to make the aperture stabilize and converge to 0.5-0.9 nm.

[0054] (4) The processing will automatically terminate when Δd ≤ 0.02 nm and RMS (surface roughness at the hole edge) ≤ 0.30 nm; where Δd is the difference between the actual hole diameter and the target hole diameter.

[0055] After processing, at least 30 pores were statistically analyzed, satisfying μ∈[0.50,0.90] nm, σ≤0.10 nm, and drift rate≤0.02 nm·h. -1 (That is, in no fewer than 30 prepared sub-nanopores, the average pore size of all pores is within the target range of 0.50-0.90 nm, and the difference (standard deviation) between pore sizes cannot exceed 0.10 nm, indicating that the process of the present invention has extremely high consistency and stability).

[0056] In a preferred embodiment of the present invention, the windowed Si3N4 chip refers to a micro / nano structure chip in which an opening window is formed on a silicon substrate by micromachining, and a 10-50 nm thick silicon nitride (Si3N4) suspension film is retained in the opening window region; the opening window is formed by KOH wet etching or deep silicon etching, supported by a silicon frame around it, and an ultrathin Si3N4 film in the center, which is used to support the two-dimensional heterojunction thin film and provide the high transparency and high mechanical stability required for transmission electron and ion beam processing.

[0057] In a preferred embodiment of the present invention, a two-dimensional heterojunction thin film is grown using chemical vapor deposition (CVD). The heterojunction consists of an upper insulating layer and a lower conductive layer. The two-dimensional heterojunction thin film is selected from h-BN / graphene, MoS2 / graphene, WS2 / MoSe2, or BP / h-BN.

[0058] In a preferred embodiment of the present invention, the preparation method of h-BN / graphene is as follows: first, a monolayer of graphene is grown on a copper foil using low-pressure chemical vapor deposition (LPCVD); then, a monolayer of hexagonal boron nitride (h-BN) is grown on a sapphire substrate using atmospheric pressure chemical vapor deposition (APCVD); subsequently, using PMMA as a support layer, the h-BN layer is covered onto the graphene surface through a wet transfer process to form a vertically stacked h-BN / graphene heterojunction; after etching with NaOH or KOH solution to release the substrate, it is rinsed and finally transferred to a windowed Si3N4 chip, and annealed at 100 °C to improve the interface bonding quality.

[0059] In a preferred embodiment of the present invention, the preparation method of MoS2 / graphene is as follows: first, monolayer graphene is grown on copper foil by CVD; then, monolayer molybdenum disulfide (MoS2) is grown on SiO2 / Si substrate by vapor phase sulfidation process, with a Mo precursor thin layer of 0.3-1 nm thickness pre-deposited before sulfidation to ensure monolayer growth; subsequently, monolayer MoS2 is peeled off from SiO2 / Si substrate using PMMA support and wet-transferred to the graphene surface to form MoS2 / graphene heterojunction; annealing is performed to remove interface residues, ensuring clean heterojunction and lattice continuity.

[0060] In a preferred embodiment of the present invention, the preparation method of WS2 / MoSe2 is as follows: a monolayer of WS2 with a higher bandgap and a monolayer of MoSe2 are grown on a SiO2 / Si substrate by CVD, wherein WS2 is prepared by simultaneous heating and sulfurization of WO2 precursor and sulfur powder, and MoSe2 is prepared by vapor-phase selenization of MoO3 and Se powder; the WS2 film is transferred to the surface of the MoSe2 film using a PMMA support layer, and a vertical two-dimensional heterojunction structure is formed by precise alignment; annealing is carried out at 300-350 °C in an Ar / H2 atmosphere to improve the heterojunction interface bonding and lattice matching.

[0061] In a preferred embodiment of the present invention, the preparation method of BP / h-BN is as follows: high-quality few-layer black phosphorus (BP) sheets are obtained on a SiO2 / Si substrate using a mechanical exfoliation method, and all operations are performed in a nitrogen glove box to avoid oxidation; subsequently, the CVD-grown monolayer h-BN is wet-transferred to the BP surface under PMMA support to form a BP / h-BN heterojunction structure. The h-BN layer also acts as a protective layer to prevent the oxidation and degradation of BP and to improve its stability under STEM irradiation. Finally, annealing is performed at 80-120 °C to remove moisture and stress.

[0062] A 3 wt% polymethyl methacrylate (PMMA) solution was spin-coated onto the surface of a two-dimensional heterojunction film and cured at 120 °C for 5 min. Then, the substrate was etched and released in a 1 mol / L KOH solution. After rinsing, the PMMA-heterojunction film was transferred to a windowed Si3N4 chip with a window thickness of 10-50 nm using a wet transfer method. After transfer, the film was annealed at 100 °C for 2 h to remove stress and obtain a smooth film surface. Subsequently, the film was washed sequentially with acetone, ethanol, and deionized water to obtain a complete and crack-free heterojunction film.

[0063] In a preferred embodiment of the present invention, the HIM processing parameters are: beam current 2-5 pA, dose 10-50 nC / μm. 2 Dwell time: 0.1-5 ms.

[0064] In a preferred embodiment of the present invention, step (2) of preparing nanopores with an initial pore size of 1-3 nm on the product obtained in step (1) using HIM is as follows: the product obtained in step (1) is placed in the cavity of a helium ion microscope (HIM), and the target window is located under a low magnification (<1000×) field of view, and then gradually magnified to 1000×. 5 To achieve initial aperture formation, appropriate beam current and dose parameters are set. The appropriate beam current and dose parameters are: beam current 2-5 pA, dose 10-50 nC / μm. 2 The dwell time is 0.1-5 ms. After processing with optimized parameters, circular pores with a diameter of 1-3 nm can be obtained on the heterostructure film. The lattice at the pore edge is continuous and the damage area is minimized, providing a uniform pore structure basis for subsequent in-situ convergence.

[0065] In a preferred embodiment of the present invention, after being transferred into the STEM cavity, the STEM accelerating voltage is 60-200 kV and the closed-loop period is ≤100 ms.

[0066] In a preferred embodiment of the present invention, Δd is determined by mapping HAADF image intensity to aperture using lattice constant and gold nanoclusters, with an aperture error ≤ 0.05 nm.

[0067] In a preferred embodiment of the present invention, the HIM and STEM are connected via a vacuum channel.

[0068] In a preferred embodiment of the present invention, when step (3) is transferred into the STEM cavity, the transfer time is ≤5 minutes.

[0069] In a preferred embodiment of the present invention, step (3) involves transferring the product obtained in step (2) into a STEM cavity, acquiring real-time images of the aperture region in HAADF (High Angle Annular Dark Field) mode, and adjusting the beam current density and scanning path through threshold determination and PID adaptive algorithm to stabilize the aperture at 0.5-0.9 nm. The step is as follows: the product obtained in step (2) is subjected to vacuum (cavity pressure ≤ 10... -6 The mbar channel is seamlessly transferred into the scanning transmission electron microscope (STEM) chamber (transfer time ≤ 5 minutes). Real-time images of the aperture area are acquired in high-angle annular dark field (HAADF) mode to obtain the image intensity matrix I(r). The system calculates the instantaneous aperture (d) based on the pre-calibrated "image intensity-aperture" mapping relationship. t The electron beam current density, residence time, and scanning trajectory (including point, arc, and ring scanning modes) are compared with the target aperture (d0 (0.5-0.9 nm)) to obtain the deviation (Δd). The control logic dynamically adjusts the electron beam current density, residence time, and scanning trajectory (including point, arc, and ring scanning modes) according to the Δd value, so as to promote the controllable migration and reconstruction of atoms at the aperture edge. The entire control process can be realized through the image feedback module and adaptive scanning function built into the traditional STEM equipment without additional hardware structure. When Δd ≤ 0.02 nm and the aperture edge surface roughness (RMS) ≤ 0.30 nm, the aperture convergence is determined to be complete (the aperture stably converges to 0.5-0.9 nm) and irradiation is terminated.

[0070] In this invention, the size and morphology of at least 30 independent nanopores were statistically analyzed. The results showed that the average pore size (μ) was in the range of 0.50-0.90 nm, the standard deviation σ ≤ 0.10 nm, and the edge RMS ≤ 0.30 nm. Furthermore, under continuous energizing at a bias voltage of +200 mV in a 1 mol / L KCl solution for 24 h, the pore size drift rate was less than 0.02 nm·h. -1 This demonstrates that the sub-nanopores prepared by the method of this invention possess excellent structural and electrochemical stability.

[0071] This invention achieves controllable convergence of sub-nanometer pore sizes in two-dimensional heterojunction materials by combining high-intensity molecular imaging (HIM) precision drilling with real-time feedback control via STEM. This method avoids the problems of unpredictable pore sizes and high edge roughness associated with traditional TEM drilling, yielding single-pore structures with continuous lattice boundaries and stable dimensions. The fabricated pore structures can be widely applied in fields such as single-molecule recognition, ion sieving, and highly sensitive biosensing, providing a high-precision and reproducible new method for the fabrication of sub-nanometer scale devices.

[0072] Embodiments of the present invention also provide a closed-loop control system for implementing the above method, as shown in the schematic diagram. Figure 1As shown, it includes: a HIM pore-forming module for fabricating initial nanopores of 1-3 nm on two-dimensional heterojunction films, including beam current setting, dose control, scan path generation, and window region positioning, forming high-roundness, low-damage initial pores to provide a controllable starting structure for subsequent Å-level convergence; a STEM processing and metrology module for acquiring pore area images in real time in HAADF mode and calculating the instantaneous pore size based on the image intensity matrix; simultaneously performing electron beam current, residence time, and scan trajectory adjustment to achieve in-situ convergence processing and morphology metrology within the pore size range of 0.5-0.9 nm; a controller module for performing threshold identification, PID adjustment, and adaptive scanning algorithms; and a data recording module for visualizing and statistically analyzing the pore size convergence process. The HIM (High-Intensity Imaging) pore-forming module and the STEM (Structured Electromechanical) processing and metrology module are physically connected via an ultra-high vacuum channel, enabling seamless transfer of initial pore samples under vacuum conditions. HAADF (High-Intensity Aperture Function) images and pore size metrology data generated by the STEM processing and metrology module are transmitted in real-time to the controller module via a high-speed data link. The controller module then establishes bidirectional communication with both the HIM and STEM modules via a control bus, enabling the distribution of key parameters such as beam current, residence time, and scanning path, as well as real-time feedback of processing status. The data recording module is connected to the controller module via a network or local bus to record and visualize the input parameters, feedback signals, and final results throughout the pore-forming process. Through this structural arrangement, the system can sequentially complete initial pore formation, in-situ metrology, closed-loop convergence, and statistical verification on the same platform, achieving automated and highly repeatable fabrication of sub-nanometer two-dimensional heterostructure nanopores within the 0.5–0.9 nm pore size range.

[0073] Embodiments of the present invention also provide a sub-nanometer two-dimensional heterojunction nanoporous device prepared according to the above-described preparation method. The sub-nanometer two-dimensional heterojunction nanoporous device has a pore size range of 0.5-0.9 nm, an edge RMS ≤ 0.30 nm, and a drift rate ≤ 0.02 nm·h. -1 .

[0074] Embodiments of the present invention also provide the application of the above-described sub-nanometer two-dimensional heterojunction nanopore device in DNA sequencing.

[0075] Embodiments of the present invention also provide the application of the above-described sub-nanometer two-dimensional heterojunction nanoporous devices in ion sieving.

[0076] Embodiments of the present invention also provide the application of the above-described sub-nanometer two-dimensional heterojunction nanoporous devices in the detection of environmental composite pollutants.

[0077] Unless otherwise specified, the room temperature in this invention is 25±2℃.

[0078] All raw materials used in the embodiments of the present invention were obtained through commercial purchase.

[0079] It should be noted that all aspects not described in detail in this invention are conventional operating methods in the field and are not the focus of this invention. For example, specific methods such as recovering adsorbents through magnetic analysis are all accomplished using conventional methods.

[0080] The technical solution of the present invention will be further illustrated by the following embodiments.

[0081] Example 1: Preparation and Transfer of h-BN / graphene Heterojunction Thin Films

[0082] This embodiment provides a transfer method based on h-BN / graphene heterojunction thin films. The overall process diagram is shown below. Figure 2 As shown, the components are: 11-NaOH solution, 101-copper foil, 102-graphene, 103-polymethyl methacrylate (PMMA), 104-sapphire, 105-monolayer hexagonal boron nitride (h-BN), and 106-silicon nitride (Si3N4). The specific steps are as follows:

[0083] First, monolayer graphene was grown on copper foil using chemical vapor deposition (CVD). The specific steps were as follows: A 25 μm thick high-purity copper foil (purity >99.8%) was placed in a quartz tube reactor and heated to 1030 °C for 30 min under a protective atmosphere of argon and hydrogen (Ar flow rate 500 sccm, H2 flow rate 50 sccm) to remove the surface oxide layer and increase the copper grain size. Then, methane was introduced as the carbon source at a flow rate of 10 sccm and a reaction pressure of 500 Pa. Growth was carried out at 1030 °C for 15 min to form a monolayer graphene film on the copper surface. After growth, the methane was turned off and the temperature was lowered to room temperature under a hydrogen atmosphere to suppress the formation of multilayer carbon structures and increase the monolayer ratio.

[0084] Secondly, a monolayer of h-BN was grown on a sapphire substrate using chemical vapor deposition. The specific steps are as follows: The polished c-side sapphire substrate was placed in an atmospheric pressure CVD furnace and heated to 1000-1100 ℃ under the protection of argon flow rate of 400 sccm and hydrogen flow rate of 50 sccm. After the temperature stabilized, triethylboron (TEB, diluted in argon at a flow rate of 3 sccm) and ammonia (NH3, 35 sccm) were introduced and reacted for 20 min to form a monolayer of hexagonal boron nitride film on the substrate surface. After the growth was completed, the supply of TEB and NH3 was stopped, and the substrate was naturally cooled to room temperature in an argon atmosphere to obtain an h-BN film with a continuous lattice and a monolayer thickness.

[0085] Then, a PMMA-assisted transfer process was used to coat the h-BN layer onto the graphene surface to form a heterojunction structure. The specific steps are as follows: A sapphire substrate with grown h-BN was spin-coated with a 3 wt% PMMA solution (3000 rpm, 60 s) and cured on a hot plate at 120 ℃ for 5 min to form a stable support layer; subsequently, the sample was immersed in a 1 mol / L KOH solution for substrate etching. After the sapphire was completely dissolved and removed, the PMMA / h-BN film automatically floated on the solution surface. The floating film was rinsed multiple times with deionized water to remove residual etching solution, and then the PMMA / h-BN film was coated onto the previously prepared graphene / copper foil surface using a wet transfer method; subsequently, it was annealed at 100 ℃ for 2 h to enhance the interfacial bonding between h-BN and graphene and to relieve some stress. After the interface stabilizes, the PMMA / h-BN / graphene composite structure is immersed in acetone for 30 min to remove PMMA, then washed with ethanol and deionized water in sequence and dried with nitrogen to obtain a completely covered h-BN / graphene heterojunction film.

[0086] The h-BN / graphene heterojunction-based thin film prepared in this embodiment is intact, crack-free, and has a smooth surface (see...). Figure 3 (a) , Raman spectrum ( Figure 4 ) and Selected Area Electron Diffraction (SAED) Pattern Figure 5 This indicates that the heterojunction film maintains a single-layer structure, has good interfacial bonding, and high crystal quality, making it suitable as a substrate for subsequent HIM initial hole processing and STEM closed-loop convergence. It can be used to fabricate high-integrity two-dimensional heterojunction chips.

[0087] Example 2: Preparation and Transfer of MoS2 / graphene Heterojunction Thin Films

[0088] This embodiment provides a method for the preparation and transfer of MoS2 / graphene heterojunction thin films to verify the universality of the method for different two-dimensional heterojunction systems.

[0089] First, monolayer graphene was grown on copper foil using chemical vapor deposition (CVD). A 25 μm thick copper foil with 99.8% purity was placed in a quartz tube CVD furnace and heated to 1030 °C for 30 min under a protective atmosphere of argon (500 sccm) and hydrogen (50 sccm). Methane was then introduced as the carbon source at a flow rate of 10 sccm and a reaction pressure of 500 Pa. Growth was continued at 1030 °C for 15 min to form a continuous monolayer graphene film. After growth, the methane flow rate was turned off, while maintaining a hydrogen flow rate of 50 sccm and allowing the film to cool naturally to room temperature to suppress the formation of multilayer structures.

[0090] Subsequently, a monolayer MoS2 was prepared on a SiO2 / Si substrate. First, a 0.5 nm thick Mo metal precursor thin film was deposited by electron beam evaporation; then, the sample was placed in a sulfurization furnace and sulfurized at a reaction temperature of 750 °C for 10 min in an environment of sulfur vapor generated by heating sulfur powder to 200 °C, to obtain a monolayer MoS2 film.

[0091] Subsequently, a monolayer of MoS2 was peeled from the SiO2 / Si substrate and wet-transferred to the surface of the previously prepared graphene film using a PMMA support layer. The specific process was as follows: a 3 wt% PMMA solution was spin-coated onto the MoS2 film surface (3000 rpm, 60 s), and cured at 120 ℃ for 5 min; the sample was immersed in a hydrofluoric acid buffered etchant (BHF) to remove the SiO2 layer, allowing the PMMA / MoS2 structure to float; after multiple rinsings, it was wet-coated onto the graphene / copper foil surface and dried at room temperature.

[0092] After the transfer was completed, the sample was placed in an Ar / H2 (95 / 5, volume ratio) mixed atmosphere and annealed at 300 °C for 1 h to enhance the bonding quality of the heterojunction interface and remove residual solvent and surface stress.

[0093] The final result is a flat and continuous MoS2 / graphene heterojunction film with a complete structure and clean interface, which can be directly used for HIM pre-forming and STEM loop closure convergence processing.

[0094] Example 3: Preparation and Transfer of WS2 / MoSe2 Heterojunction Thin Films

[0095] This embodiment provides another method for preparing and stacking two-dimensional heterojunction thin films (WS2 / MoSe2) to further verify the applicability of the pore-forming method of the present invention to different material systems.

[0096] First, a monolayer of WS2 was grown on a SiO2 / Si substrate. The substrate was placed in a CVD reactor, and the W source for WS2 was WO2 powder. Its evaporation temperature was set to 900 ℃, and the sulfur powder temperature was set to 200 ℃. After heating to the set temperature under an argon atmosphere, it was held for 12 min to form a continuous monolayer WS2 film on the substrate surface.

[0097] Subsequently, a monolayer of MoSe2 was grown. The MoO3 precursor was placed in the upstream region, with its evaporation temperature set at 750 °C and the Se powder temperature set at 300 °C. A monolayer MoSe2 film was deposited on the substrate under the influence of an argon gas flow for 10 min.

[0098] Subsequently, the two monolayer films were heterojunction-stacked. The specific steps were as follows: a 3 wt% PMMA solution was spin-coated onto the WS2 film (3000 rpm, 60 s) and cured at 120 ℃ for 5 min; the sample was immersed in BHF etching solution to remove the SiO2 layer, allowing the PMMA / WS2 structure to float on the solution surface. After rinsing, the PMMA / WS2 structure was applied to the surface of the monolayer MoSe2 film using a wet alignment method under an optical microscope, ensuring that its lattice orientation matched the stacked region.

[0099] After alignment, the mixture is annealed at 320 °C for 1 h in an Ar / H2 (95 / 5, volume ratio) atmosphere to eliminate interfacial bubbles, improve stack flatness, and enhance the bonding quality of the heterojunction interface.

[0100] After annealing, soak in acetone solution for 30 minutes to remove PMMA, and then wash with ethanol and deionized water in sequence.

[0101] Finally, a continuous, flat, and crack-free WS2 / MoSe2 heterostructure film was obtained with good interface quality. It can obtain 1-3 nm initial pores under the HIM initial pore processing conditions in Example 4, and further converge to the sub-nanometer pore size range through STEM closed-loop control.

[0102] It should be noted that for heterojunction materials such as MoS2 / graphene and WS2 / MoSe2, their optical micrographs, Raman images, and initial pore morphologies show no substantial structural difference from the heterojunction films prepared in Example 1. This demonstrates that the method of the present invention is universally applicable to different two-dimensional heterojunction systems.

[0103] Example 4: HIM Pre-hole Preparation Process

[0104] This embodiment demonstrates a method for achieving high-precision initial hole machining on heterojunction thin films using helium ion microscopy (HIM).

[0105] The h-BN / graphene heterojunction film obtained in Example 1 was placed in the HIM sample chamber and evacuated to 10 °C. -6 mbar;

[0106] The window area was located at a low magnification (<1000×), and then gradually magnified to 120k×. Specifically, the chip was first observed and the window area located at a 60k× field of view, followed by sequential magnification to 80k×, 100k×, and 120k×. Figure 6 The beam current was set at 3 pA and the dose at 25 nC·μm. -2 The dwell time is 1 ms;

[0107] After processing, circular initial pores with a diameter of approximately 1.5-2.0 nm were obtained. The lattice at the pore edge was continuous, and no obvious collapse or cracks were observed. Figure 3 As shown in (b).

[0108] By adjusting the combination of beam current and dose, primary pore structures of different sizes in the range of 1-3 nm can be obtained (see...). Figure 7 The details are as follows:

[0109] The beam current was set to 2 pA and the dose to 15 nC·μm. -2 Under these conditions, ion bombardment is weak, the amount of atoms removed from the film is small, and a minimum initial pore size of approximately 1.0-1.2 nm is formed.

[0110] The beam current was set to 3 pA and the dose to 25 nC·μm. -2 This parameter combination can form round, lattice-continuous primary pores with a diameter of approximately 1.5-1.7 nm on two-dimensional heterojunction films.

[0111] The beam current was increased to 4 pA, and the dose was set to 35 nC·μm. -2 The higher beam current resulted in more atoms being removed layer by layer, increasing the aperture to approximately 2 nm.

[0112] The beam current was set to 5 pA, and the dose was increased to 45 nC·μm. -2 Under these conditions, the ion beam etching rate is significantly increased, and initial holes approaching 3 nm in size can be formed.

[0113] Example 5: STEM Closed-Loop Convergence and Aperture Control

[0114] Based on Example 4, the initial well sample was vacuum transferred to the scanning transmission electron microscope (STEM) chamber (ensuring a transfer time ≤ 5 minutes), and sub-nanopore closed-loop convergence control was implemented. After transfer to the STEM, the accelerating voltage was set to 80 kV, and the operation was carried out with a closed-loop control period of 50-80 ms to ensure the synchronization of real-time image intensity acquisition and aperture feedback adjustment.

[0115] Images of the aperture region were acquired in real time using high-angle annular dark-field (HAADF) imaging mode, and the current aperture d was calculated using the image intensity versus aperture calibration curve. t The deviation Δd is obtained by comparing it with the target aperture d0 = 0.7 nm.

[0116] The system automatically adjusts the beam current (initial intensity of 15 pA), residence time (100 μs), and scanning path through the control logic module to achieve dynamic adaptive adjustment.

[0117] The mapping between HAADF image intensity and pore size was used to calibrate the pore size error using lattice constants and gold nanoclusters. The specific process was as follows: High-resolution images of a region with a known lattice constant of the two-dimensional material were acquired in HAADF mode. A pixel-to-actual length conversion coefficient was obtained using Fast Fourier Transform (FFT). Subsequently, gold nanoclusters (0.5-2.0 nm in diameter) with pre-calibrated diameters by TEM were deposited in the same region, and their HAADF image intensities were acquired to establish an "image intensity-size" correspondence. Using the gold nanoclusters as a standard reference, the integral value of the HAADF image intensity of the nanopore was substituted into the fitted curve to calculate the corresponding pore size. After repeating the calibration 20 times, the pore size calibration error was determined to be ≤0.05 nm. This error was used in real-time to judge Δd during closed-loop control. Irradiation was automatically stopped when Δd ≤ 0.02 nm. Finally, stable pores with a pore size of approximately 0.7 ± 0.05 nm and an edge smoothness RMS ≈ 0.25 nm were obtained (see Figure 7).

[0118] For example, the image pair of the closed loop before and after the hole Figure 8 As shown, the aperture is clearly reduced and the edge structure is regular.

[0119] Test Example 1: Aperture Convergence Law and Statistical Validation

[0120] To verify the repeatability and controllability of the method of the present invention, statistical analysis was performed on 30 independent well samples.

[0121] Under the same HIM pre-pore conditions (beam current of 3 pA, dose of 25 nC·μm), -2 The aperture was converged to the target aperture of 0.7 nm using STEM closed-loop control.

[0122] The aperture convergence process and statistical distribution results are shown in the figure below. Figure 9 As shown, (a) is the convergence curve of pore size over time, and (b) is a statistical graph of 30 pore samples. The statistical results show that the pore size steadily converges from 1.8 nm to 0.740 nm (standard deviation σ = 0.080 nm), and the final pore size distribution is concentrated.

[0123] The above results indicate that the method of the present invention has high repeatability and sub-nanometer level control accuracy.

[0124] Test Example 2: λ-DNA Molecular Detection Experiment Based on Heterojunction Subnanopores

[0125] A heterojunction nanopore chip (pore size approximately 1.0 ± 0.1 nm) converged via STEM closed-loop control was immobilized in an electrochemical detection cell. Both sides of the cell contained 1 mol / L KCl, and the buffer solution was 10 mmol / L Tris-HCl (pH = 8.0). The experimental temperature was 25 °C. Ag / AgCl electrodes were inserted on both sides of the system, and a +200 mV voltage was applied to drive DNA molecules through the pores. The signal acquisition system used an Axopatch 200B amplifier and a Digidata 1550B data acquisition card, with a sampling frequency of 100 kHz and a low-pass filter of 10 kHz.

[0126] The experimental results are shown in Figure 10. The upper side is the baseline current of 100mV λ-DNA (concentration of 10 ng / μL), and the curve is stable with no obvious blocking signal. The lower side is the detection signal of 200mV λ-DNA (concentration of 10 ng / μL), and multiple transient current pulse events can be seen, indicating that DNA molecules sequentially cause transient blocking through the sub-nanopore.

[0127] This indicates that the heterojunction subnanopore prepared by this invention has high sensitivity and low noise characteristics, and can reliably identify single-stranded DNA molecules at the electrical signal level, verifying its application potential in the field of biomolecular detection.

[0128] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing sub-nanometer two-dimensional heterostructure nanopores based on HIM pre-formed pores and STEM closed-loop control, characterized in that, Includes the following steps: (1) Transferring a two-dimensional heterojunction thin film on a windowed Si3N4 chip; (2) Using HIM to prepare nanopores with an initial pore size of 1-3 nm on the product obtained in step (1); (3) Transfer the product obtained in step (2) into the STEM cavity, acquire the image of the pore area in real time in HAADF mode, and adjust the beam density and scanning path through threshold determination and PID adaptive algorithm to make the pore size stably converge to 0.5-0.9 nm. (4) The processing will automatically terminate when Δd ≤ 0.02 nm and RMS ≤ 0.30 nm; where Δd is the difference between the actual aperture and the target aperture. HIM processing parameters are: beam current 2-5 pA, dose 10-50 nC / μm. 2 Dwell time: 0.1-5 ms; After being transferred into the STEM cavity, the STEM acceleration voltage is 60-200 kV and the closed-loop period is ≤100 ms. Δd was determined by mapping HAADF image intensity to aperture using lattice constant and gold nanoclusters, with an aperture error ≤ 0.05 nm; When transferring the material into the STEM cavity in step (3), the transfer time should be ≤5 minutes; The sub-nanometer two-dimensional heterostructure nanopores have a pore size range of 0.5-0.9 nm, an edge RMS ≤ 0.30 nm, and a drift rate ≤ 0.02 nm·h. -1 .

2. The method for preparing sub-nanometer two-dimensional heterostructure nanopores based on HIM pre-formed pores and STEM closed-loop control according to claim 1, characterized in that, HIM and STEM are connected via a vacuum channel.

3. A sub-nanometer two-dimensional heterojunction nanoporous device, characterized in that, The sub-nanometer two-dimensional heterojunction nanoporous device prepared according to any one of claims 1-2 has a pore size range of 0.5-0.9 nm, an edge RMS ≤ 0.30 nm, and a drift rate ≤ 0.02 nm·h. -1 .

4. The application of a sub-nanometer two-dimensional heterojunction nanoporous device as described in claim 3 in DNA sequencing.

5. The application of the sub-nanometer two-dimensional heterojunction nanoporous device as described in claim 3 in ion sieving.

6. The application of the sub-nanometer two-dimensional heterojunction nanoporous device as described in claim 3 in the detection of environmental composite pollutants.

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