Preparation method of complex oxide interface one-dimensional system

Abstract

The invention discloses a preparation method of a complex oxide interface one-dimensional system. According to the method, a pulse laser deposition technology is utilized, based on a step structure of a substrate, a novel one-dimensional nano material of a complex oxide is prepared through a growth mode of flowing along a step, and the method comprises the steps that a material S is epitaxially grown on the substrate, the thickness of the material S is one step height, and the transverse width of the material S is L1; a material B is laterally and epitaxially grown on the substrate or the material S along the edge of the new step, the lateral width is L2, and the thickness is the height of one step; taking L1 + L2 as a period, and repeatedly growing for n periods; the steps are repeated, N repetitions are achieved in the longitudinal direction, and then preparation of the complex oxide novel interface one-dimensional system is achieved. The method disclosed by the invention develops a new material interface regulation and control way, can be popularized to other associated systems, and lays a physical foundation for research and development of all-oxide spinning electronic devices.

Description

Technical Field

[0001] The invention belongs to the technical field of thin film growth, and in particular relates to a method for preparing a one-dimensional system of a complex oxide interface. Background Art

[0002] Complex oxide superlattices have made significant achievements in the fields of physical state control and two-dimensional physics, such as interface-induced superconductivity, multiferroicity, two-dimensional electron gas, metal-insulator phase transition, magnetoelectric coupling effect, etc. However, most complex oxide superlattices currently form vertical structures through layered growth. The present invention aims to greatly enhance the flexibility of artificial control through lateral structures, design regions of different materials within a single-layer structure, and thus advance the interface advantages of oxides to a new level. Summary of the invention

[0003] In view of the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a method for preparing a one-dimensional system of a complex oxide interface using pulsed laser deposition technology. The method of the present invention can design different material regions with different proportions in a single-layer structure with a lateral interface of two materials to enhance the ability to control the physical state and study the evolution of new one-dimensional systems. The preparation technology of the lateral film of the present invention has opened up a new method for controlling the interface of complex oxide films, which can be extended to all other related systems, laying a physical foundation for the research and development of all-oxide spintronic devices.

[0004] The technical solution of the present invention is specifically described as follows.

[0005] The present invention provides a method for preparing a one-dimensional system of a complex oxide interface, which uses a pulsed laser deposition method to prepare a one-dimensional system of a complex oxide on a single crystal substrate with a step structure; the size of one dimension of the three dimensions of the complex oxide is smaller than the mean free path of molecules; and the method comprises the following steps: 1) placing a single crystal substrate with a step width of L into a growth chamber of a pulsed laser deposition system, placing a target material S and a target material B into a target stage of the pulsed laser deposition system, wherein the target material S and the target material B are both oxides, wherein at least the target material B is a non-volatile oxide; 2) Heat the substrate to T1, adjust the oxygen pressure to P1, rotate the target stage to the position of the target material S, and adjust the pulse laser energy E1, frequency F1 and focus position X1; 3) epitaxially grow material S on the substrate with a thickness of 1 step height and a lateral width of L1; 4) Changing the substrate temperature T2, adjusting the oxygen pressure P2, rotating the target stage to the position of the target material B, changing the pulse laser energy E2, the pulse laser frequency F2 and the focus position X2, and based on step 3), epitaxially growing material B on the substrate or on the material S along the new edge step, with a lateral width of L2 and a thickness of 1 step height; 5) Take L1+L2 as a cycle and repeat the growth for n cycles; 6) Repeat steps 2) to 5) to achieve N repetitions in the longitudinal direction, thereby achieving the preparation of a novel complex oxide interface one-dimensional system.

[0006] In the present invention, the distance between the target and the substrate is controlled to be less than 5 cm.

[0007] In the present invention, under the conditions of temperature T1, oxygen pressure P1, laser energy E1, and frequency F1, the material S can grow epitaxially on the substrate in layers or flow along the steps.

[0008] In the present invention, under the conditions of temperature T2, oxygen pressure P2, laser energy E2, and frequency F2, material B can flow and grow on the substrate or on material S along the steps.

[0009] In the present invention, at least the target material S is a non-volatile oxide, and the target material A can be a volatile oxide or a non-volatile oxide; the material that can achieve flow growth along the step can be an island-like growth or layered growth material, and flow growth along the step can be achieved by increasing the growth temperature. However, since the saturated vapor pressure of some elements is very high, the increase in temperature will cause the elements to volatilize and cause component segregation. Such materials cannot achieve flow growth along the step by increasing the temperature. For example, volatile materials such as Pb and Bi cannot achieve flow growth along the step by increasing the temperature.

[0010] In the present invention, the substrate is a SrTiO3 (001) substrate or a NdGaO3 (001) substrate, the target material S is SrRuO3, and the target material B is BiFeO3.

[0011] In the present invention, L1≤L, L2 <L。

[0012] The single-layer structure in the present invention refers to the layer with a transverse interface between the S material and the B material. If the S material grows a complete layer and the B material grows a strip, there will be a transverse interface between S and the strip B. This transverse interface is the one-dimensional interface chain.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The present invention no longer limits the growth mode of all oxide materials on the substrate to satisfy flow growth, which greatly reduces the difficulty of material growth and has a larger window for material selection, providing greater possibilities for exploring more material properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a pulse laser deposition system in an embodiment of the present invention.

[0015] Figure 2 It is a step substrate required in the embodiment of the present invention, such as SrTiO3(001), NGO(001) and other substrates that can be processed with step surfaces.

[0016] Figure 3 Schematic diagram of growing the first layer of SrRuO3 thin film on a SrTiO3 (001) step substrate in an embodiment of the present invention, where SrRuO3 is marked as S; (a) layered growth mode, (b) step flow growth.

[0017] Figure 4 This is a schematic diagram of preparing BiFeO3 strips by following the step flow growth mode after growing SrRuO3 in an embodiment of the present invention, where BiFeO3 is marked as B; (a) step flow growth on material S, (b) step flow growth on substrate.

[0018] Figure 5 Schematic diagram of a one-dimensional interface system of [BiFeO3 / SrRuO3]2 formed by repeating two cycles in the longitudinal direction in an embodiment of the present invention; (a) S grows in layers, and B grows in step flow on material S; (b) both material S and material B grow in step flow.

[0019] Figure 6 It is a schematic diagram of the growth of a one-dimensional system of an oxide interface in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] In order to make the technical solution of the present invention clearer, the following is further described in detail in conjunction with the accompanying drawings and examples. It should be understood that the embodiments described below are only used to explain the present invention and are not intended to limit the present invention. What is described below is a part of multiple possible embodiments of the present invention, which is intended to provide a basic understanding of the present invention, and is not intended to confirm the key or decisive elements of the present invention or to limit the scope of protection.

[0021] Figure 6The figure is a schematic diagram of the growth of a one-dimensional system of an oxide interface in an embodiment of the present invention; the present invention proposes a method for preparing a new type of one-dimensional system of a complex oxide interface. The growth method includes: a substrate screening stage, an oxide material growth rate exploration stage, and a main layer growth stage. The method uses an atomic force microscope (AFM) to screen substrates with flat surfaces, obvious steps, and moderate step widths. In the stage of exploring the growth rate of oxide materials, based on the growth dynamics of the screened substrate and the pulsed laser deposition system (PLD), the growth mode of the oxide on the substrate surface is adjusted by controlling the substrate temperature and the oxygen pressure of the main chamber, adjusting the energy, frequency, and focusing of the laser to achieve a mode in which the oxide material flows and grows along the steps. At the same time, the number of laser pulses for each layer of growth is accurately adjusted to determine the actual growth rate of the oxide. The main layer growth stage is based on the conditions for the oxide to flow and grow along the steps in the second stage, and the width of the lateral epitaxial growth of the material along the steps is controlled by accurately adjusting the number of pulsed lasers. By changing the number of pulses, the composition ratio of different materials in the same layer can be achieved, thereby achieving the structure of the one-dimensional system.

[0022] The preparation method of the novel complex oxide interface one-dimensional system of the present invention has no strict requirements on the material to be grown, but has strict requirements on the substrate.

[0023] The substrate used in this example is a single crystal SrTiO3 (100) with a step, a miscut angle of < 0.1°, a step width of L = 240 nm, and a step layer thickness of one unit cell; Figure 2 As shown. The grown materials are BiFeO3 and SrRuO3, and the laser wavelength used is 248 nm. The specific preparation steps of the interface one-dimensional system in this example are as follows: Place BiFeO3 and SrRuO3 targets in Figure 1 The target stage of the pulsed laser deposition system (PLD) main chamber growth chamber shown in the figure requires the vacuum degree of the main chamber growth chamber to reach 5 × 10⁻ 9 mbar. Oxygen was introduced into the main chamber through the oxygen tube until the oxygen pressure reached 2 × 10⁻ 5 mbar, set the wavelength to 248 nm and the energy density of the laser to 1 mj / cm 2 and a frequency of 5 Hz. The focusing lens position is adjusted (a focusing lens with a focal length of 50 cm is used in this example), where the distances between the target stage of BiFeO3 and SrRuO3 and the focusing lens are 49.5 cm and 50.2 cm respectively, and the corresponding lens position scales on the lens guide rail are 435 and 442 respectively. Under this condition, the impurities on the surface of the BiFeO3 and SrRuO3 targets are removed by laser bombardment.

[0024] Place the cleaned SrTiO3 substrate on the sample holder, introduce nitrogen, open the sample transfer chamber, place the sample holder on the sample transfer rod, and use the sample transfer rod to transfer the sample holder to the sample holder of the main chamber of the pulsed laser deposition system (PLD). Adjust the focusing lens position to 442, the distance between the sample holder and the target stage is 4 cm, the target stage is switched to the SrRuO3 target position and the target stage is turned on. Then adjust the oxygen pressure in the main chamber growth chamber to the growth oxygen pressure of 1.5 × 10⁻¹ mbar, turn on the infrared laser to gradually heat the substrate to 680℃ at a rate of 5℃ / min. Reset the laser parameters: laser energy 200 mJ, frequency 2Hz. Under the above conditions, Figure 3 (a) shows that the number of laser pulses required to grow a complete layer of SrRuO3 film in a layered growth mode is 200 pulses. In addition, SrRuO3 can also grow in a flow growth mode along the step to grow half the step width. For P1 = 100 pulses, the lateral epitaxial width of the SrRuO3 film is 120nm (half the step width), and the vertical height is one step thickness, as shown in Figure 3 (b).

[0025] On the basis of the above, the oxygen pressure and substrate temperature of the main chamber growth chamber are kept unchanged, the target stage is adjusted to the BiFeO3 target position, and the laser parameters are reset: laser energy 160 mJ, frequency 1 Hz, and the focusing lens position is changed to 435. Under the above conditions, Figure 4 The step flow growth of a half-layer BiFeO3 film on a SrRuO3 film requires 60 pulses. The film has a lateral epitaxial width of 120nm and a vertical height of one atomic layer.

[0026] Taking P1 + P2 as a growth cycle, repeat the above experimental operation and repeat 2 cycles in the longitudinal direction, that is, a one-dimensional interface system of [BiFeO3 / SrRuO3]2 is formed on the SrTiO3 (100) substrate, as shown in Figure 5 shown.

[0027] Due to the precise control of each component of each single layer of two groups of materials in the system structure, SrRuO3 material can grow in layers or flow along the steps, and BiFeO3 material strictly flows along the steps. The resulting BiFeO3 and SrRuO3 interface one-dimensional system material has high crystal quality and few defects. Moreover, the interface of BiFeO3 and SrRuO3 is directly exposed on the surface, providing a powerful means for direct and in-situ detection of the properties of the interface. In addition, the growth method of the oxide interface one-dimensional system can be combined with the vertical growth method to achieve full control of the multi-dimensional material.

[0028] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for preparing a one-dimensional system of a complex oxide interface, characterized in that: The method uses a pulsed laser deposition method to prepare a one-dimensional system of a complex oxide interface on a single crystal substrate with a step structure; the size of one of the three dimensions of the complex oxide is smaller than the mean free path of the molecule; and comprises the following steps: 1) placing a single crystal substrate with a step width of L into a growth chamber of a pulsed laser deposition system, placing a target material S and a target material B into a target stage of the pulsed laser deposition system, wherein the target material S and the target material B are both oxides, wherein at least the target material B is a non-volatile oxide; 2) Heat the substrate to T1, adjust the oxygen pressure to P1, rotate the target stage to the position of the target material S, and adjust the pulse laser energy E1, frequency F1 and focus position X1; 3) epitaxially grow material S on the substrate with a thickness of 1 step height and a lateral width of L1; 4) Changing the substrate temperature T2, adjusting the oxygen pressure P2, rotating the target stage to the position of the target material B, changing the pulse laser energy E2, the pulse laser frequency F2 and the focus position X2, and based on step 3), epitaxially growing material B on the substrate or on the material S along the new edge step, with a lateral width of L2 and a thickness of 1 step height; 5) Take L1+L2 as a cycle and repeat the growth for n cycles; 6) Repeat steps 2) to 5) to achieve N repetitions in the longitudinal direction, thereby achieving the preparation of a novel complex oxide interface one-dimensional system.

2. The method for preparing a one-dimensional system of a complex oxide interface according to claim 1, characterized in that: The distance between the target materials S, B and the substrate was controlled to be less than 5 cm.

3. The method for preparing a one-dimensional system of a complex oxide interface according to claim 1, characterized in that: Under the conditions of temperature T1, oxygen pressure P1, laser energy E1 and frequency F1, material S can grow along the step edge or grow layer-by-layer epitaxially on the substrate, causing the step edge to move laterally.

4. The method for preparing a one-dimensional system of a complex oxide interface according to claim 1, characterized in that: Under the conditions of temperature T2, oxygen pressure P2, laser energy E2 and frequency F2, material B can grow along the new step edge on the substrate.

5. The method for preparing a one-dimensional system of a complex oxide interface according to claim 1, characterized in that: The substrate is a SrTiO3 (001) substrate or a NdGaO3 (001) substrate, the target material S is SrRuO3, and the target material B is BiFeO3.

6. The method for preparing a one-dimensional system of a complex oxide interface according to claim 1, characterized in that: L1≤L,L2 <L。 7. A one-dimensional complex oxide interface system prepared according to the preparation method according to any one of claims 1 to 6.

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