Preparation method of lanthanum-calcium-manganese-oxygen thin film material

Abstract

The invention discloses a preparation method of a lanthanum calcium manganese oxide thin film material, and belongs to the technical field of photoelectric detection materials. The preparation method comprises the following steps: (1) preparing a precursor solution, namely dissolving La (NO3) 3.6 H2O, Ca (NO3) 2.4 H2O and Mn (NO3) 2 in ethylene glycol monomethyl ether, adding a chelating agent and a dispersing agent, and sequentially stirring and aging the mixed liquid to obtain the precursor solution; (2) substrate pretreatment: cleaning and drying the LaAlO3 substrate in sequence; (3) spin-coating a wet film: spin-coating the precursor solution to the surface of the substrate through three-stage spin-coating to obtain the wet film; (4) wet film drying: performing three-stage drying on the wet film, and repeating the steps (3) and (4) for three times; and (5) sintering: sequentially performing pre-sintering and final sintering on the dried film to obtain the lanthanum-calcium-manganese-oxygen film. The thin film prepared by the method has excellent TCR and Tk values, the Curie temperature of the thin film can be changed in a wide temperature range, and the method has important beneficial effects on practical application of the LCMO thin film.

Description

Technical Field

[0001] The invention belongs to the technical field of photoelectric detection materials and relates to a method for preparing a lanthanum calcium manganese oxide thin film material. Background Art

[0002] Lanthanum calcium manganese oxide film (LaCaMnO3, abbreviated as LCMO film) is a ferromagnetic functional material. LCMO film has relatively excellent physical properties, such as giant magnetoresistance effect, metal-insulator transition, phase separation, etc. Therefore, LaCaMnO3 is considered to have great application potential in magnetic sensors, refrigerators, and uncooled infrared detectors, and has high application value.

[0003] The temperature coefficient of resistance (TCR) of LCMO films directly affects their performance in uncooled infrared detectors. TCR indicates the material's sensitivity to temperature and determines the feasibility of LCMO film applications in uncooled infrared detectors as well as the sensitivity of uncooled infrared detectors. However, the TCR of existing LCMO films is relatively low, which greatly limits their practical application in uncooled infrared detectors.

[0004] Therefore, it is necessary to provide a preparation method of lanthanum calcium manganese oxide thin film material, and to improve the TCR of LCMO film by optimizing the preparation method of thin film material so as to make it have better application performance. Summary of the Invention

[0005] In order to overcome the problems in the background technology, the present invention optimizes the preparation process of the LCMO film, thereby effectively improving the TCR of the LCMO film. The TCR of the film material of the present invention can reach up to 27.86%K -1 , and its corresponding T k 241.60K, T k The closer the value is to room temperature, the higher the TCR value of the LCMO film at room temperature, which means that the sensitivity of the LCMO film working at room temperature is higher. k The closer the value is to room temperature, the better the working performance of the uncooled infrared detector at room temperature, and its uncooled advantages can be more fully utilized.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0007] The present invention provides a method for preparing a lanthanum calcium manganese oxide thin film material, the preparation method comprising the following steps:

[0008] (1) Preparation of precursor solution: La(NO3)3·6H2O, Ca(NO3)2·4H2O, and Mn(NO3)2 are dissolved in ethylene glycol methyl ether at a molar ratio of La(NO3)3·6H2O:Ca(NO3)2·4H2O:Mn(NO3)2=0.7:0.3:1, and a chelating agent and a dispersant are added. The mixed liquid is stirred and aged in turn to obtain a precursor solution.

[0009] (2) Substrate pretreatment: The LaAlO3 (LAO) substrate is cleaned and dried in sequence;

[0010] (3) spin coating a wet film: spin coating the precursor solution obtained in step (1) onto the surface of the substrate pretreated in step (2) through three-stage spin coating to obtain a wet film;

[0011] (4) Drying the wet film: The wet film obtained in step (3) is dried in three stages, and steps (3) and (4) are repeated three times. Since the spin coating in step (3) is divided into three stages, and the drying in step (4) is divided into three stages, steps (3) and (4) are repeated in the following manner: first, the first stage of spin coating is completed, then the first stage of drying is performed, and then step (3) is repeated to perform the second stage of spin coating and the second stage of drying, and finally step (3) is repeated to perform the third stage of spin coating and the third stage of drying, thereby repeating steps (3) and (4) three times to complete the entire spin coating and drying process.

[0012] (5) Sintering: Pre-sintering and final sintering are performed on the thin film dried in step (4) to obtain a lanthanum calcium manganese oxide thin film.

[0013] Preferably, in step (1), the chelating agent is citric acid, and the molar ratio of the added amount of the chelating agent to the total amount of La(NO3)3·6H2O, Ca(NO3)2·4H2O, and Mn(NO3)2 is chelating agent:total amount=1:4.

[0014] Preferably, in step (1), the dispersant is ethylene glycol, and the molar ratio of the amount of the dispersant added to the total amount of La(NO3)3·6H2O, Ca(NO3)2·4H2O, and Mn(NO3)2 is dispersant:total amount=1:4.

[0015] Preferably, in step (1), the solid-liquid ratio of the total amount of La(NO3)3·6H2O, Ca(NO3)2·4H2O, and Mn(NO3)2 to ethylene glycol methyl ether is total amount: ethylene glycol methyl ether = 1:5.

[0016] Preferably, in step (1), the stirring time is 6 hours and the aging time is 24 hours.

[0017] Preferably, in step (2), the specific process of cleaning the LaAlO3 substrate is: using acetone solution to perform ultrasonic vibration cleaning on the LaAlO3 substrate twice, each cleaning time is 5 minutes, then using distilled water to clean the substrate, then wiping the substrate surface with alcohol, and then using anhydrous ethanol to perform ultrasonic vibration cleaning on the substrate twice, each cleaning time is 5 minutes, and finally rinsing the substrate with distilled water.

[0018] Preferably, in step (2), the drying temperature is 350° C. and the drying time is 1 hour.

[0019] Preferably, in step (3), the specific process of the three-stage spin coating is: first, spin coating at a speed of 600 r / min for 5 s, then spin coating at a speed of 1500 r / min for 10 s, and finally spin coating at a speed of 4000 r / min for 15 s.

[0020] Preferably, in step (4), the specific process of the three-stage drying is: first drying at 80°C for 10 minutes, then drying at 140°C for 10 minutes, and finally drying at 350°C for 30 minutes.

[0021] Preferably, in step (5), the pre-sintering temperature is 750° C., the pre-sintering time is 30 min, the final sintering temperature is 1200° C., and the final sintering time is 4 to 10 min.

[0022] Beneficial effects of the present invention:

[0023] 1. The present invention successfully prepared T by optimizing the preparation process of LCMO k =241.60K when TCR=27.86%K -1 The LCMO film has better application performance in uncooled infrared detectors.

[0024] 2. The present invention regulates the T of the LCMO film by regulating the final firing time within the range of 4 to 10 minutes. k As well as the TCR value, without causing serious negative impact on other properties of the film, LCMO films with certain differences in performance can be prepared in a simple way, so that the LCMO film has better adaptability in more subdivided application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The XRD results of the LCMO films prepared in Comparative Example 1 and Examples 1-4 of the present invention are shown;

[0026] Figure 2 IR spectra of the LCMO films prepared in Comparative Example 1 and Examples 1-4 of the present invention;

[0027] Figure 3 AFM images of the LCMO films prepared in Comparative Example 1 and Examples 1-4 of the present invention;

[0028] Figure 4 This is the XPS broad spectrum of the LCMO films prepared in Comparative Example 1 and Examples 1-4 of the present invention;

[0029] Figure 5 The resistivity-temperature curves of the LCMO films prepared in Comparative Example 1 and Examples 1-4 of the present invention;

[0030] Figure 6 The TCR and T of the LCMO films prepared in Comparative Example 1 and Examples 1-4 of the present invention are shown in Table 1. k changes. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the contents described above.

[0032] In the comparative examples and embodiments of the present invention, chemical reagents not otherwise specified were all commercially available analytically pure for the experiments.

[0033] Example 1

[0034] In this embodiment, the LCMO film was prepared by the following method:

[0035] (1) Preparation of precursor solution: La(NO3)3·6H2O, Ca(NO3)2·4H2O and Mn(NO3)2 were dissolved in ethylene glycol methyl ether in a molar ratio of La(NO3)3·6H2O:Ca(NO3)2·4H2O:Mn(NO3)2=0.7:0.3:1, wherein the solid-liquid ratio of the total amount of La(NO3)3·6H2O, Ca(NO3)2·4H2O and Mn(NO3)2 to ethylene glycol methyl ether was total amount:ethylene glycol methyl ether=1:5, and citric acid and ethylene glycol were added according to the ratio of chelating agent: total amount=1:4 and dispersant: total amount=1:4, respectively. The mixed liquid was stirred for 6 hours and aged for 24 hours to obtain a precursor solution.

[0036] (2) Substrate pretreatment: The LaAlO3 substrate was ultrasonically cleaned twice with acetone solution for 5 minutes each time. The substrate was then rinsed with distilled water. The substrate surface was then wiped with alcohol. The substrate was ultrasonically cleaned twice with anhydrous ethanol for 5 minutes each time. Finally, the substrate was rinsed with distilled water. The rinsed substrate was then placed in a box-type sintering furnace and dried at 350°C for 1 hour. The substrate was removed and allowed to cool naturally to room temperature before use.

[0037] (3) Spin coating a wet film: Place the substrate on the workbench of the spin coater, use a dropper to absorb the precursor solution and drop it onto the surface of the substrate, start the spin coater, first spin coat at a speed of 600 r / min for 5 s, then spin coat at a speed of 1500 r / min for 10 s, and finally spin coat at a speed of 4000 r / min for 15 s. After the spin coating is completed, a wet film is obtained.

[0038] (4) Drying of wet film: First, the wet film was placed in a corundum boat and the corundum boat was placed in a drying oven and dried at 80°C for 10 min. Then the temperature was raised to 140°C and dried for another 10 min. Finally, the wet film was placed in a box-type sintering furnace and dried at 350°C for 30 min to obtain a dry gel film.

[0039] Repeat the above steps (3) and (4) three times.

[0040] (5) Sintering: The dry gel film was placed in a tube furnace and pre-sintered at 750 °C for 30 min. The sintering temperature was then raised to 1200 °C and sintered for 6 min to obtain the LCMO film, which was recorded as La 0.7 Ca 0.3 MnO3 film.

[0041] Example 2

[0042] This embodiment adopts the same method as the embodiment to prepare the LCMO thin film, except that: in this embodiment, the final sintering time is 4 minutes.

[0043] Example 3

[0044] This embodiment adopts the same method as the embodiment to prepare the LCMO thin film, except that: in this embodiment, the final sintering time is 8 minutes.

[0045] Example 4

[0046] This embodiment adopts the same method as the embodiment to prepare the LCMO thin film, except that: in this embodiment, the final sintering time is 10 minutes.

[0047] Comparative Example 1

[0048] In this comparative example, the LCMO thin film was prepared by the same method as in the embodiment, except that in this comparative example, the final sintering time was 2 minutes.

[0049] The crystal structures of the LCMO films prepared in Examples 1-4 and Comparative Example 1 were tested, and the results are shown in Table 1.

[0050] Table 1

[0051]

[0052] Through Table 1 and Figure 1 It can be seen that the crystal structures of the thin film samples prepared in Examples 1-4 and Comparative Example 1 are all Pnma structures, and all thin film samples are epitaxially grown along the LAO substrate for preferential orientation. This shows that this preparation method can effectively optimize the TCR and T k value.

[0053] pass Figure 2 It can be seen that the preparation method of the present invention does not affect the change of the Mn-O bond length.

[0054] pass Figure 3 It can be seen that the average roughness of the film samples prepared in Examples 1-4 and Comparative Example 1 is relatively small, indicating that the film prepared by the preparation method of the present invention has a dense surface and is a polycrystalline film. At the same time, the crystallization quality of the film is the best when the final firing time is 6 minutes.

[0055] The electrical transport performance of the thin film samples prepared in Examples 1-4 and Comparative Example 1 was tested, and the results are shown in Table 2.

[0056] Table 2

[0057]

[0058] Through Table 2 and Figure 4 It can be seen that the Mn ions in the film sample are in the form of Mn 3+ and Mn 4+ There are two forms, Mn 4+ The percentage of content increases with the increase of final firing time. Figure 5 and Figure 6 It can be seen that the longer the final firing time is, the better it is. The TCR of the sample fired at 1200℃ for 6 minutes is 27.86%K -1 , corresponding to T k It is 241.60K, with the best performance.

[0059] In summary, the LCMO film prepared by the preparation method of the present invention has excellent TCR and T k value, and its Curie temperature can be changed in a wide temperature range, which has an important beneficial impact on the practical application of LCMO films.

[0060] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for preparing a lanthanum calcium manganese oxide thin film material, characterized in that: The preparation method comprises the following steps: (1) Preparation of precursor solution: La(NO3)3·6H2O, Ca(NO3)2·4H2O, and Mn(NO3)2 are dissolved in ethylene glycol methyl ether in a molar ratio of La(NO3)3·6H2O:Ca(NO3)2·4H2O:Mn(NO3)2=0.7:0.3:1, and a chelating agent and a dispersant are added. The mixed liquid is stirred and aged in sequence to obtain a precursor solution; (2) Substrate pretreatment: The LaAlO3 substrate is cleaned and dried in sequence; (3) spin coating a wet film: spin coating the precursor solution obtained in step (1) onto the surface of the substrate pretreated in step (2) through three-stage spin coating to obtain a wet film; (4) Drying the wet film: performing three-stage drying on the wet film obtained in step (3), and repeating steps (3) and (4) three times; (5) Sintering: Pre-sintering and final sintering are performed on the thin film dried in step (4) to obtain a lanthanum calcium manganese oxide thin film.

2. The preparation method according to claim 1, wherein: In the step (1), the chelating agent is citric acid, and the molar ratio of the added amount of the chelating agent to the total amount of La(NO3)3·6H2O, Ca(NO3)2·4H2O, and Mn(NO3)2 is chelating agent:total amount=1:

4.

3. The preparation method according to claim 1, wherein: In the step (1), the dispersant is ethylene glycol, and the molar ratio of the amount of the dispersant added to the total amount of La(NO3)3·6H2O, Ca(NO3)2·4H2O, and Mn(NO3)2 is dispersant:total amount=1:

4.

4. The preparation method according to claim 1, wherein: In the step (1), the solid-liquid ratio of the total amount of La(NO3)3·6H2O, Ca(NO3)2·4H2O, and Mn(NO3)2 to ethylene glycol methyl ether is total amount: ethylene glycol methyl ether = 1:

5.

5. The preparation method according to claim 1, wherein: In the step (1), the stirring time is 6 hours and the aging time is 24 hours.

6. The preparation method according to claim 1, wherein: In the step (2), the specific process of cleaning the LaAlO3 substrate is as follows: using acetone solution to perform ultrasonic vibration cleaning on the LaAlO3 substrate twice, each cleaning time is 5 minutes, then using distilled water to clean the substrate, then wiping the substrate surface with alcohol, and then using anhydrous ethanol to perform ultrasonic vibration cleaning on the substrate twice, each cleaning time is 5 minutes, and finally rinsing the substrate with distilled water.

7. The preparation method according to claim 1, wherein: In the step (2), the drying temperature is 350° C. and the drying time is 1 hour.

8. The preparation method according to claim 1, wherein: In the step (3), the specific process of the three-stage spin coating is: first, spin coating at a rotation speed of 600 r / min for 5 s, then spin coating at a rotation speed of 1500 r / min for 10 s, and finally spin coating at a rotation speed of 4000 r / min for 15 s.

9. The preparation method according to claim 1, wherein: In step (4), the specific process of the three-stage drying is: first drying at 80°C for 10 minutes, then drying at 140°C for 10 minutes, and finally drying at 350°C for 30 minutes.

10. The preparation method according to claim 1, characterized in that: In the step (5), the pre-sintering temperature is 750° C., the pre-sintering time is 30 minutes, the final sintering temperature is 1200° C., and the final sintering time is 4 to 10 minutes.

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