CN114516615A

CN114516615A - Preparation method of high-stability graphene nanopore

Info

Publication number: CN114516615A
Application number: CN202210143912.9A
Authority: CN
Inventors: 刘智波; 郭浩炜; 田建国
Original assignee: Nankai University
Current assignee: Nankai University
Priority date: 2022-02-17
Filing date: 2022-02-17
Publication date: 2022-05-20

Abstract

This patent introduces a method for preparing graphene nanopores with high stability. Transferring the high-quality graphene film prepared by a mechanical stripping method to a silicon nitride chip with a hole to form a suspended film structure. Lattice defects are manually introduced into the graphene film through oxygen plasma etching, and the defect density in the graphene is accurately controlled and used for attaching to generate nano holes. And placing the processed graphene chip in a special light-operated fluid pool, and applying gradually-increased pulse current to two sides for breakdown. In the breakdown process, pulsed laser is used for irradiating the graphene in the target area to improve the lattice temperature of the graphene and improve the occurrence probability of breakdown events. The graphene nanopore prepared by the method has high size controllability, the minimum breakdown diameter is below 1nm, the highest control precision of the pore diameter is 0.5nm, and the highest control precision of the pore length is 0.34 nm. Compared with the traditional solid nano-pore, the pore size stability is obviously improved, and the good structural consistency can be still kept in the soaking test for 1 month. Soaking in 1M KCl (pH 8) solution, and increasing pore diameter daily by less than 0.7%.

Description

Preparation method of high-stability graphene nanopore

Technical Field

The invention belongs to the field of biosensing and two-dimensional materials, and relates to a preparation method and a matching device of a high-stability graphene nanopore.

Background

Highly stable, dimensionally accurate, extremely thin-thickness nanopores are critical to ultrasensitive molecular biosensors and high efficiency ion filters. The solid nanopore which is common at present is stable in the continuous measurement processQualitative results can only be maintained for a few hours. Meanwhile, during long-term storage, the pore structure is usually irreversibly changed due to brownian motion and chemical corrosion of the solution. Specifically, the pore diameter becomes gradually larger with time. This is due to the SiN as nanoporous carrier film_x、SiO₂、Al₂O₃Etc. the defect density is high, and the size of the nano-pore is continuously increased under the physical/chemical erosion of the solution. Poor stability limits the wide use of nanopores in long-cycle testing and complex environments.

Two-dimensional (2D) materials with atomic thickness and excellent mechanical properties offer a new choice for nanopores. The preparation method of the two-dimensional material nanopore comprises a Transmission Electron Microscope (TEM), a Focused Ion Beam (FIB), a Controlled Breakdown (CBD) and the like. However, the single-layer two-dimensional material nanopore prepared by the method has no obvious advantage in stability. The reason is that the higher defect density in two-dimensional materials prepared by Chemical Vapor Deposition (CVD), which is currently widely used, exacerbates nanopore instability. Therefore, how to prepare structurally highly stable nanopores in two-dimensional materials while maintaining the spatial resolution advantage is a challenge of current research.

Disclosure of Invention

The invention aims to provide a technical route for preparing stable nano holes on a high-quality mechanical stripping graphene film and accurately controlling the size of the stable nano holes.

In order to achieve the purpose, the method comprises the following steps:

firstly, preparing a silicon nitride chip with holes by using a semiconductor processing technology;

secondly, preparing high-quality thin-layer graphene on a silicon wafer by using a mechanical stripping method;

thirdly, transferring the graphene to a window of a silicon nitride chip with a hole prepared in advance in a fixed point manner by using PDMS;

fourthly, processing the graphene suspended film by utilizing oxygen plasma etching, manually introducing lattice defects, monitoring the defect density through Raman spectrum, and accurately controlling the introduction amount of the defects;

fifthly, irradiating the graphene film in the target area by using pulse laser to improve the breakdown probability of the graphene film;

and sixthly, applying gradually increased pulse current to two sides of the graphene film by using a digital source meter to perform breakdown.

Drawings

Fig. 1 is a schematic diagram of a process for preparing a high-stability graphene nanopore;

FIG. 2 is a schematic view of a photoinduced electrical breakdown device;

FIG. 3 is a graph of data comparing the breakdown characteristics of treated and untreated samples during electrical breakdown;

FIG. 4 is a transmission electron micrograph of a thin graphene nanopore;

fig. 5 is a graph of comparative data on the stability of graphene nanopores and silicon nitride nanopores.

Detailed Description

In order to further illustrate the present invention, the displacement amplification techniques provided by the present invention are described in detail below by way of the accompanying drawings and examples, which should not be construed as limiting the scope of the invention. The materials and instruments used in the following examples are commercially available. In addition, any methods and materials similar or equivalent to those described herein can be used in the methods of the present invention.

Example 1

Preparation and treatment of high-quality graphene suspended membrane structure

As shown in FIG. 1, firstly, high-quality few-layer graphene is peeled from natural graphite crystal to silicon wafer (SiO) by using Sigao tape₂Si) substrate, determining whether its thickness and structural integrity are suitable by atomic force microscopy; then covering PDMS on the target sample, and dripping deionized water into the gap between PDMS and the silicon wafer to separate the sample from the substrate; picking up PDMS/graphene, and accurately transferring the PDMS/graphene to a pre-prepared silicon nitride chip with holes (with the aperture of 2um) through two-dimensional material fixed-point transfer equipment to form a suspended graphene film; placing the chip with the graphene suspended film with the back facing upwards into an oxygen plasma cleaning machine (YZD08-2C), adjusting the power to be 17.1% and etching for 10s, wherein the gas source is high-purity oxygen; after the treatment is finished, the Raman spectrum is used for detecting the suspended film Whether the film defect density meets the requirement or not so as to carry out the next breakdown process.

Example 2

Preparation of graphene nanopore by photoinduced electrical breakdown

After being modulated into 300Hz pulse light by a chopper by using a 532nm laser, the pulse light is focused on the surface of the graphene film by a 50-time long-focus objective lens, the average light power is adjusted to 10mW by an attenuation sheet, and the specific device is shown in figure 2. Pulse current is applied to two sides of the graphene film through a digital source meter (Keithley 2450B), the initial current is 10 muA, the step length of each pulse is increased by 5 muA, the pulse duration is 0.2s, and the data acquisition frequency is 30 Hz. Both pore size and conductance measurements were measured by a patch clamp amplifier (HEKA EPC100 USB) with a data acquisition frequency of 50 kHz. Fig. 3a shows the breakdown curves of graphene nanopores treated and untreated with artificial defect introduction, and fig. 3b shows the initial breakdown pore size comparison of treated and untreated samples. It can be clearly observed that the processed sample is more accurate in the control accuracy of the aperture. Figure 4 shows 2nm diameter graphene (thickness about 1.5nm) nanopores prepared with this technique.

Example 3

Nanopore structure stability test

The prepared nanopore was immersed in a 1M KCl (pH ═ 8) solution, and the liquid phase environment used for the long-time measurement was simulated, with the temperature being kept around room temperature (25 ℃). The nanopore device is tested once every 12h, and the sample is in a completely sealed state in the storage process so as to reduce the influence of solution volatilization on the pore structure. The solution in the Flowcell was replaced with a new KCl solution for each test, minimizing measurement errors. The aperture change range of the thin-layer graphene nanopore prepared by the method is far smaller than that of a single-layer graphene nanopore and a silicon nitride nanopore prepared by the same method, and the average daily aperture increase range is smaller than 0.7%.

Claims

1. A preparation method of a high-stability graphene nanopore is characterized in that high-quality graphene is prepared through a mechanical stripping method and transferred to a silicon nitride chip with a hole to form a graphene suspended membrane structure; the defect density in the graphene suspended film is accurately controlled through oxygen plasma etching, so that the nano-pores can grow depending on the defects; the target area is irradiated by pulse light, so that the breakdown voltage of the graphene film is reduced; the thin film is broken down by setting increasing pulse current, and then high-stability graphene nano holes are generated.

2. The method as claimed in claim 1, wherein the prepared nanopore is not limited to graphene, and other two-dimensional material nanopores such as molybdenum disulfide, tungsten diselenide, and black phosphorus can be prepared by using the technology.

3. The method of claim 1, wherein the plasma etching gas is not limited to only a source of high purity oxygen. Other gases commonly used, depending on the material, e.g. nitrogen, argon, CF₄And the mixed gas of the plasma etching gas and the mixed gas in a certain proportion can be used as a gas source for plasma etching.

4. The method according to claim 1, characterized in that the current source selected for the electric breakdown process can be replaced by other power supply devices of the same type or having similar functions.

5. The method of claim 1, wherein the laser wavelength, pulse frequency, average power, and optics model and objective magnification in the optical path can be modified to achieve the same effect.

6. The method as claimed in claim 1, wherein the silicon nitride chip with holes for preparing the graphene suspended membrane structure can be replaced by devices with holes, such as carbon films with holes, metal micro-grids and the like with similar functions and structures.