CN115506009A - A method for preparing in-situ nitrogen-doped epitaxial oxide single crystal thin film - Google Patents

Abstract

The invention provides a method for preparing an in-situ nitrogen-doped epitaxial oxide single crystal thin film, comprising: cleaning the substrate, placing the substrate in the chamber of a pulsed laser deposition device, feeding a mixture of oxygen and nitrogen, and waiting for the atmosphere in the chamber to After being uniform and stable, the pure oxide target is used for pulse laser deposition on the substrate. After the deposition is completed, annealing is performed in the same atmosphere. By adopting the technical scheme of the present invention, by adjusting the atmosphere during epitaxial growth, the doping of nitrogen element can be realized, and the preparation of doped oxide film can be realized without selecting a specific target material, and the method is simple and effective; no secondary treatment of the film is involved , will not cause damage to the prepared high-quality films.

Description

A method for preparing in-situ nitrogen-doped epitaxial oxide single crystal thin film

technical field

The invention relates to the field of material technology, in particular to a method for preparing an in-situ nitrogen-doped epitaxial oxide single crystal thin film.

Background technique

Oxide thin film materials have played an important role in the development of modern science and technology. At present, many technologies have been developed for the preparation of functional oxide films, such as solution method, spin coating method, magnetron sputtering, molecular beam deposition, pulsed laser deposition, etc. Among them, pulsed laser deposition (PLD), as a popular thin film epitaxial growth method, has many advantages, such as high film crystal quality and stable stoichiometric ratio. Nitrogen doping plays a significant role in regulating the functional behavior of oxide films, such as regulating the phase transition temperature and on-off ratio of vanadium dioxide films. Since PLD technology is often used for the epitaxial growth of thin films in an oxygen environment, the nitrogen-doped target method is often used for the nitrogen doping of thin films, that is, the method of selecting a target material that has been doped with nitrogen, or some post-processing methods, such as ion implantation , Ammonia treatment, etc. Among them, the nitrogen-doped target method is to perform epitaxial growth by pre-sintering a nitrogen-doped target. Ion implantation is mainly to use the prepared oxide film sample, place it in a high vacuum, and then achieve nitrogen doping by N ion beam bombardment; ammoniation treatment is to place the prepared oxide film in an ammonia atmosphere and high temperature Under these conditions, nitrogen doping is achieved.

Although the doped epitaxial growth of oxide films can be achieved by bombarding nitrogen-doped targets, there are two problems. First, the content of nitrogen doping is the same as that of the target. Continuous adjustment is realized during the epitaxial growth process; secondly, some targets are not easy to be fired after nitrogen doping, and the cost is higher than that before undoped. Nitrogen doping is simple and effective as a post-treatment method, but the post-treatment method often destroys the crystal quality of the original epitaxial growth film and affects the functional properties of the film. At present, the bottleneck in the preparation of high-quality epitaxial nitrogen-doped functional oxide thin film materials is that there is no preparation method that can achieve in-situ nitrogen-doped growth. Compared with oxygen, nitrogen has lower activity and stronger bond energy. It is difficult for conventional vapor deposition preparation methods to separate nitrogen into nitrogen ions and participate in the film deposition process. At present, there is no disclosure of relevant content on the research on the introduction of nitrogen to regulate the performance of thin films in PLD technology.

Contents of the invention

In view of the above technical problems, the present invention discloses a method for preparing an in-situ nitrogen-doped epitaxial oxide single crystal thin film. The obtained thin film has high epitaxial quality and achieves a certain content of doping, thereby realizing the performance regulation of the functional oxide thin film , and meet its needs in materials science research and engineering applications.

To this end, the technical scheme adopted in the present invention is:

A method for preparing an in-situ nitrogen-doped epitaxial oxide single crystal thin film, comprising: cleaning the substrate, placing the substrate in the cavity of a pulsed laser deposition device, feeding a mixture of oxygen and nitrogen, and after the atmosphere in the cavity is uniform and stable, The pure oxide target is used for pulse laser deposition on the substrate. After the deposition is completed, annealing is carried out in the same atmosphere.

With this technical solution, by adjusting the gas environment in the PLD cavity during epitaxial growth, nitrogen doping can be realized while epitaxially growing high-quality single-crystal oxide films. As the pulsed laser bombards the surface of the target, the bursting plasma plume has extremely high energy. When it collides with the nitrogen gas molecules in the cavity, it can ionize the gas molecules into a mixture of atoms, ions, and electrons, and transmit them to The surface of the substrate material, thus participating in the epitaxial growth of the film. Since this is an in-situ growth technique, there is no need for post-doping treatment, which effectively guarantees the crystal quality of the film. In addition, by properly adjusting the atmosphere in the cavity, the same target can be continuously adjusted with different nitrogen doping concentrations.

As a further improvement of the present invention, the oxide is vanadium dioxide. By adopting this technical scheme, the metal-insulator transition temperature of the vanadium dioxide thin film is reduced by nitrogen doping, and the higher the doping concentration, the greater the reduction of the phase transition temperature.

As a further improvement of the present invention, the material of the substrate is titanium dioxide.

As a further improvement of the present invention, the condition parameters of pulsed laser deposition are: temperature 380-420°C, total pressure in the cavity 15-25mTorr, laser energy density 1.0-1.2J/cm2, pulse frequency 10 Hz. Further preferably, the condition parameters of the pulsed laser deposition are: temperature 400°C, total pressure in the cavity 20 mTorr, laser energy density 1.1 J/cm2, pulse frequency 10 Hz.

As a further improvement of the present invention, after the deposition is completed, it is annealed after being kept in the original epitaxial atmosphere for 5 minutes.

As a further improvement of the present invention, the mixture of oxygen and nitrogen is introduced, and the volume ratio of oxygen and nitrogen is 1:1. By adopting this technical scheme, by controlling the volume ratio of oxygen and nitrogen to be 1:1, ideal metal-insulator transition performance can be obtained.

Compared with prior art, the beneficial effect of the present invention is:

First, by adopting the technical solution of the present invention, the doping of nitrogen element can be realized by adjusting the atmosphere during epitaxial growth, and the preparation of doped oxide film can be realized without selecting a specific target material. The method is simple and effective; Secondary treatment will not damage the prepared high-quality film.

Second, compared with other existing technologies, the nitrogen-doped vanadium dioxide thin film prepared by the technical scheme of the present invention not only regulates the metal-insulator transition temperature, but also effectively improves the crystal quality. This effect comes from the introduction of nitrogen, not only for Doping provides a source of nitrogen and also provides internal forces for the film growth process, enabling it to reduce the lattice mismatch. In particular. Under the optimized nitrogen and oxygen atmosphere conditions, nitrogen-doped vanadium dioxide has a lower transition temperature and maintains a higher on-off ratio, and is expected to be applied to high-performance smart switching devices.

Description of drawings

Fig. 1 is the XRD contrast graph of the film deposited in Examples 1-3 of the present invention and Comparative Examples 1-2.

Fig. 2 is the microscopic topography figure of the film deposited in Examples 1-3 of the present invention and Comparative Examples 1-2.

Fig. 3 is the XPS comparison diagram of the films deposited in Examples 1-3 of the present invention and Comparative Examples 1-2.

Fig. 4 is a comparison chart of the N content of the films deposited in Examples 1-3 of the present invention and Comparative Examples 1-2.

Fig. 5 is the temperature resistance curves of the films deposited in Examples 1-3 and Comparative Examples 1-2 of the present invention.

FIG. 6 is a comparison chart of XRD of the films deposited in Example 1 and Comparative Example 3 of the present invention.

FIG. 7 is the temperature resistance curves of the films deposited in Example 1 and Comparative Example 3 of the present invention.

detailed description

The preferred embodiments of the present invention will be further described in detail below.

Example 1

Titanium dioxide is selected as the substrate and cleaned and dried. Before depositing the film, enter the atmosphere into the PLD cavity, and use the flowmeter to control the ratio of oxygen and nitrogen entering the cavity, control the volume ratio of oxygen and nitrogen to 1:1, and keep it for 10 minutes. After the atmosphere in the cavity is uniform and stable , the pure target of vanadium dioxide is pulsed laser deposited on the titanium dioxide substrate by means of pulsed laser deposition technology, and after the film deposition is completed, it is kept in this atmosphere for 5 minutes, and then annealed in the same atmosphere.

Example 2

On the basis of Example 1, in this example, the volume ratio of oxygen and nitrogen is 2:1.

Example 3

On the basis of Example 1, in this example, the volume ratio of oxygen and nitrogen is 1:2.

Comparative example 1

On the basis of Example 1, in this comparative example, the gas introduced was pure nitrogen.

Comparative example 2

On the basis of Example 1, in this comparative example, the gas introduced was pure oxygen.

The XRD comparison diagram of the films obtained in Examples 1~3 and Comparative Examples 1~2 is shown in Figure 1, the SEM comparison diagram is shown in Figure 2, the energy spectrum comparison diagram is shown in Figure 3, and the N content comparison diagram is shown in Figure 3. As shown in 4, it can be seen that under the same nitrogen and oxygen ratio environment, the method of the embodiment can realize the effective regulation of the nitrogen doping content from about 0% to 4%.

The temperature resistance curves of the films obtained in Examples 1-3 and Comparative Examples 1-2 are shown in Figure 5. It can be seen that the metal-insulator transition temperature of the vanadium dioxide film is reduced by nitrogen doping, and the higher the doping concentration , the lower the phase transition temperature is. Under the condition that the volume ratio of nitrogen and oxygen is 1:1, the ideal metal-insulator transition performance can be obtained.

Comparative example 3

On the basis of Example 1, the difference of this comparative example is that the ratio of oxygen and nitrogen varies during the deposition process. Specifically, during the deposition process, the flow ratio of nitrogen and oxygen to the cavity changes instantaneously, and the ratio of nitrogen gas is first reduced to a volume ratio of nitrogen and oxygen of 0.5:1, and then recovered after 2 minutes.

The XRD comparison diagram of the films deposited in Example 1 and Comparative Example 3 is shown in Figure 6, and the temperature resistance curve is shown in Figure 7. It can be seen that the ratio of nitrogen and oxygen gas in Comparative Example 1 fluctuates, and the obtained sample is not a single-phase structure, and The metal-insulator transition performance of the obtained thin film is worse, specifically showing that the transition is not sharp, and the temperature range is more relaxed; it presents multi-stage transitions; and the transition switching ratio is reduced. It can be seen that the fluctuation of the air pressure can easily cause the composition of the film to be uneven, which will greatly affect the metal-insulator transition performance.

During the epitaxial growth process of the single crystal substrate, the crystal structure and lattice parameters of the single crystal substrate are the same or similar to those of the epitaxial film, and it is easier to obtain a high-quality single crystal epitaxial film. Both titanium dioxide and vanadium dioxide have a rutile structure and are similar in structure, but the lattice parameters of the two are quite different (the volume of the vanadium dioxide unit cell is smaller than that of titanium dioxide), so under normal circumstances, the vanadium dioxide unit cell can be epitaxially grown in the PLD technology. crystal, but generally the crystal quality is poor. In the doping of nitrogen element in the embodiment of the present invention, on the one hand, nitrogen ions are slightly larger than cations, causing a certain lattice expansion. During epitaxial growth, the lattice mismatch between the substrate and the substrate is reduced, which is beneficial to high-quality single The preparation of crystalline vanadium dioxide thin films; on the other hand, nitrogen doping introduces hole carriers, inhibits the V-V dimerization in the vanadium dioxide structure, plays a role in stabilizing the rutile phase, and is also conducive to maintaining its high crystal quality.

The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it cannot be assumed that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deduction or replacement can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (6)

1. A method for preparing an in-situ nitrogen-doped epitaxial oxide single crystal thin film is characterized by comprising the following steps: cleaning a substrate, placing the substrate in a cavity of pulse laser deposition equipment, introducing a mixture of oxygen and nitrogen, performing pulse laser deposition on the substrate by using a pure target material of an oxide after the atmosphere in the cavity is uniform and stable, and annealing in the same atmosphere environment after deposition is completed.

2. The method for producing an in-situ nitrogen-doped epitaxial oxide single-crystal thin film according to claim 1, wherein: the condition parameters of the pulse laser deposition are as follows: the temperature is 380 to 420 ℃, the total air pressure in the cavity is 15 to 25mTorr, and the laser energy density is 1.0 to 1.2J/cm ² And the pulse frequency is 10 Hz.

3. The method for producing an in-situ nitrogen-doped epitaxial oxide single-crystal thin film according to claim 2, characterized in that: the condition parameters of the pulse laser deposition are as follows: the temperature is 400 ℃, the total air pressure in the cavity is 20 mTorr, and the laser energy density is 1.1J/cm ² And the pulse frequency is 10 Hz.

4. The method for producing an in-situ nitrogen-doped epitaxial oxide single-crystal thin film according to claim 3, wherein: and after the deposition is finished, keeping the temperature for 5 min in the original epitaxial atmosphere environment, and then annealing.

5. The method for preparing an in-situ nitrogen-doped epitaxial oxide single crystal film according to any one of claims 1 to 4, wherein: and introducing a mixture of oxygen and nitrogen, wherein the volume ratio of the oxygen to the nitrogen is 1.

6. The method for producing an in-situ nitrogen-doped epitaxial oxide single-crystal thin film according to claim 5, wherein: the oxide is vanadium dioxide, and the substrate is made of titanium dioxide.

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