MgF2-ZnS composite film and preparation method thereof

Abstract

The invention relates to the technical field of preparation of optical films with variable infrared refractive indexes, in particular to a MgF2-ZnS composite film and a preparation method thereof. The method comprises the following steps: by taking MgF2 and ZnS as target materials, respectively mounting the target materials on two different cathodes, and simultaneously and respectively sputtering the MgF2 target and the ZnS target under a vacuum condition; placing the substrate on a sample disc perpendicular to the surface normal of the MgF2 target and the ZnS target, enabling the sample disc to rotate, enabling the substrate on the sample disc to sequentially pass through the MgF2 target and the ZnS target and to be respectively opposite to the MgF2 target and the ZnS target, and sequentially depositing MgF2 and ZnS on the substrate to form an MgF2-ZnS composite film; the sequential sputtering method provided by the invention solves the problem of shortage of S and F atoms in the film, and the refractive index of the composite film is adjustable between 1.38 and 2.13; the composite film is compact in structure and small in surface roughness and has certain hydrophobicity.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of infrared refractive index variable optical films, in particular to a MgF2-ZnS composite film and a preparation method thereof. Background Art

[0002] Infrared devices such as infrared windows, infrared lenses, and infrared reflectors are important components of infrared optical systems, and they place high demands on the refractive index and transmittance / reflection properties of infrared materials. In order for infrared optical devices to meet specific spectroscopic characteristics, high- and low-refractive-index laminated infrared optical films must be prepared on the surface of these devices. For example, infrared windows require high infrared transmittance, but commonly used infrared window materials are limited and usually have a high refractive index, such as Ge (n=3.959), Si (n=3.419), ZnSe (n=2.39), ZnS (n=2.2), spinel MgAl2O4 (n=1.73), diamond C (n=2.38), etc., resulting in large surface reflection losses (usually >10%). Depositing high- and low-refractive-index laminated anti-reflection films on the surface of infrared windows is an important method to reduce surface reflectivity and increase transmittance.

[0003] Although various thin film technologies are relatively mature and available thin film materials are also abundant, there are still relatively few available low-refractive index thin film materials. This is because most low-refractive index materials have relatively severe absorption in the mid-wave infrared (3-5μm) or long-wave infrared (8-12μm) bands. Therefore, there are fewer low-refractive index materials available in the infrared band, resulting in a relatively small number of available low-refractive index thin film materials. In addition, preparing porous or loosely structured thin film materials is a common method to reduce the refractive index of the material, but the mechanical properties such as strength and hardness of porous or loosely structured materials deteriorate; and they easily absorb water vapor, resulting in moisture absorption, causing their refractive index and optical properties to change with the ambient humidity, thereby deteriorating the performance stability of optical devices. Therefore, the development of low-refractive index thin film materials and thin film materials with variable refractive index in the low refractive index range (n<2.0) has important application value.

[0004] ZnS is a commonly used high-refractive-index infrared optical material, widely used in infrared windows, lenses, and optical thin films. MgF2 is a commonly used low-refractive-index infrared optical thin film material with high transmittance, making it widely used in optical thin film technology. A recent study reported the use of a dual-source co-evaporation technique, using electron beam evaporation of MgF2 and resistance thermal evaporation of ZnS, to prepare MgF2-ZnS composite thin films with a variable refractive index (1.42-2.07) in the visible light range. However, during the co-evaporation process, this method causes the evaporated Mg, F, Zn, and S atoms to simultaneously reach the substrate. This allows the S and F atoms to combine to form SF6 gas, which is then extracted by the vacuum system. This results in a shortage of non-metallic elements S and F in the composite film, while an excess of metallic elements Zn and Mg remains. This excess of metallic elements can lead to severe infrared absorption and a rapid deterioration of the film's infrared transmission properties. Therefore, how to solve the shortage of S and F non-metallic elements in the preparation process of MgF2-ZnS composite film, and further make the film have a lower refractive index, continuously adjustable infrared refractive index in a wider range, and higher performance stability has become a technical problem that needs to be solved urgently by technicians in this field. Summary of the Invention

[0005] The present invention aims to provide a MgF2-ZnS composite film and a preparation method thereof. A sequential sputtering method is proposed based on magnetron sputtering technology, which realizes the preparation of the MgF2-ZnS composite film and the regulation of the MgF2 and ZnS contents in the composite film. As the content ratio of MgF2 to ZnS varies within the range of 185:1 to 1:6, the refractive index of the MgF2-ZnS composite film can be adjusted between 1.38 and 2.13. The MgF2-ZnS composite film has a dense structure, low surface roughness, and certain hydrophobicity.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a MgF2-ZnS composite film, comprising the following steps:

[0008] 1) MgF2 and ZnS are used as target materials, installed on two different cathodes respectively, and sputtered simultaneously on the MgF2 target and the ZnS target under vacuum conditions;

[0009] 2) Place the substrate on a sample tray perpendicular to the normal lines of the MgF2 target and the ZnS target surface, rotate the sample tray, and allow the substrate on the sample tray to pass through the MgF2 and ZnS targets in sequence and face the MgF2 and ZnS targets respectively, thereby sequentially depositing MgF2 and ZnS on the substrate to form a MgF2-ZnS composite film;

[0010] The sputtering gas is argon, and the vacuum condition is a vacuum degree of <8×10-4 Pa.

[0011] Optionally, the flow rate of the argon gas is 5 to 10 sccm.

[0012] Optionally, the sputtering gas pressure is 0.1-0.3 Pa.

[0013] Optionally, the sputtering power of the MgF2 target is 150-200W; the sputtering power of the ZnS target is 20-100W.

[0014] Optionally, the temperature of the substrate is 80-200°C.

[0015] Optionally, the substrate passes through the MgF2 target at a speed of 1 to 6 rpm; the substrate passes through the ZnS target at a speed of 1 to 6 rpm.

[0016] The present invention also provides a MgF2-ZnS composite film prepared by the above preparation method.

[0017] Optionally, the refractive index of the MgF2-ZnS composite film is adjustable between 1.38 and 2.13.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention provides a method for preparing a MgF2-ZnS composite thin film. A sequential sputtering method is used to prevent S and F atoms from simultaneously reaching a substrate surface and combining to generate SF6 gas, thereby solving the problem of S and F atom shortage in the film and ensuring that the Mg:F and Zn:S atomic ratios in the MgF2-ZnS composite thin film are close to the stoichiometric ratios of 1:2 and 1:1, respectively. In the sequential sputtering method proposed by the present invention, a substrate repeatedly passes over MgF2 and ZnS target materials in sequence, but each passage is short, forming discontinuous MgF2 and ZnS films, respectively. The two films are uniformly dispersed and nested with each other, thereby growing a structurally uniform MgF2-ZnS composite thin film, effectively avoiding delamination or the growth of a laminated MgF2 / ZnS film.

[0020] The MgF2-ZnS composite film provided by the present invention regulates the content ratio of MgF2 to ZnS within the range of 185:1 to 1:6 by adjusting key process parameters such as Ar gas flow rate, gas pressure, substrate heating temperature, sample disk rotation rate, sputtering power of the MgF2 target, and sputtering power of the ZnS target, thereby achieving a lower refractive index and continuously adjustable infrared refractive index within a wider range (1.38 to 2.13), filling the gap in low-refractive-index materials and enriching the selectivity of low-refractive-index materials. In addition, the developed MgF2-ZnS composite film has a dense structure, low surface roughness, and certain hydrophobicity. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a cross-sectional SEM image of the MgF2-ZnS composite film prepared in Example 1;

[0022] Figure 2 This is the XPS narrow scan spectrum of Mg, F, Zn, and S of the MgF2-ZnS composite film prepared in Example 1;

[0023] Figure 3 The n and k curves of the MgF2-ZnS composite film prepared in Example 1 in the 2-12 μm band;

[0024] Figure 4 This is a water contact angle diagram of the MgF2-ZnS composite film prepared in Example 1;

[0025] Figure 5 This is a surface AFM image of the MgF2-ZnS composite film prepared in Example 2;

[0026] Figure 6 This is a cross-sectional SEM image of the MgF2-ZnS composite film prepared in Example 2;

[0027] Figure 7 This is the XPS full scan spectrum of the MgF2-ZnS composite film prepared in Example 2;

[0028] Figure 8 Surface SEM image of the MgF2-ZnS composite film prepared in Example 3;

[0029] Figure 9 This is a cross-sectional SEM image of the MgF2-ZnS composite film prepared in Example 4;

[0030] Figure 10 This is a surface AFM image of the MgF2-ZnS composite film prepared in Example 5;

[0031] Figure 11 This is the XPS full scan spectrum of the MgF2-ZnS composite film prepared in Example 5;

[0032] Figure 12 This is a surface AFM image of the MgF2-ZnS composite film prepared in Example 6;

[0033] Figure 13 Surface SEM image of the MgF2-ZnS composite film prepared in Example 7;

[0034] Figure 14 This is the XPS full scan spectrum of the MgF2-ZnS composite film prepared in Example 7;

[0035] Figure 15The n and k curves of the MgF2-ZnS composite film prepared in Example 7 in the 2-12 μm band;

[0036] Figure 16 This is the XPS full scan spectrum of the MgF2-ZnS composite film prepared in Example 8;

[0037] Figure 17 The n and k curves of the MgF2-ZnS composite film prepared in Example 8 in the 2-12 μm band;

[0038] Figure 18 This is a water contact angle diagram of the MgF2-ZnS composite film prepared in Example 8;

[0039] Figure 19 This is a curve diagram of the refractive index (n) of the MgF2-ZnS composite film at a wavelength of 10μm as a function of the MgF2 and ZnS content ratio. DETAILED DESCRIPTION

[0040] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0041] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0042] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0043] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the present invention. The present description and examples are intended to be illustrative only.

[0044] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0045] The raw materials used in the present invention can be obtained commercially or prepared using existing technologies.

[0046] The present invention provides a method for preparing a MgF2-ZnS composite film, comprising the following steps:

[0047] 1) MgF2 and ZnS are used as target materials, installed on two different cathodes respectively, and sputtered simultaneously on the MgF2 target and the ZnS target under vacuum conditions;

[0048] 2) Place the substrate on a sample tray perpendicular to the normal lines of the MgF2 target and the ZnS target surface, rotate the sample tray, and allow the substrate on the sample tray to pass through the MgF2 and ZnS targets in sequence and face the MgF2 and ZnS targets respectively, thereby sequentially depositing MgF2 and ZnS on the substrate to form a MgF2-ZnS composite film;

[0049] The sputtering gas is argon, and the vacuum condition is a vacuum degree of <8×10 -4 Pa.

[0050] In the embodiment of the present invention, the purity of MgF2 is high purity; the purity of ZnS is high purity.

[0051] In the embodiment of the present invention, a high-purity MgF2 target is first placed on a cathode target position in a vacuum chamber of a multi-target magnetron sputtering coating machine, a high-purity ZnS target is placed on another cathode target position, and a pre-treated substrate is placed on a sample tray perpendicular to the normal line of the MgF2 and ZnS target surfaces. The background vacuum is pumped to <8×10 -4 Pa; then set the substrate heating temperature, introduce Ar gas into the vacuum chamber, and set the air pressure in the vacuum chamber.

[0052] In an embodiment of the present invention, the normal lines of the MgF2 and ZnS target surfaces remain parallel.

[0053] In the present invention, argon is used as the sputtering gas to generate plasma.

[0054] In an embodiment of the present invention, the flow rate of the argon gas is 5 to 10 sccm, preferably 6 to 9 sccm, and more preferably 7 to 8 sccm.

[0055] In an embodiment of the present invention, the sputtering gas pressure is 0.1-0.3 Pa, preferably 0.12-0.25 Pa, and more preferably 0.15-0.2 Pa.

[0056] The present invention has no particular restrictions on the choice of substrate material, and any material that can be used as an infrared window can be applied to the present invention. In an embodiment of the present invention, the substrate material is preferably a Si substrate, a glass substrate or a ZnS substrate.

[0057] In an embodiment of the present invention, the substrate is also pretreated before use. The specific method is as follows: the double-sided polished substrate is first rinsed with deionized water to remove surface particles; then the surface of the substrate is wiped with absorbent cotton soaked in acetone and alcohol in turn to remove organic pollutants such as grease on the surface; then the substrate is ultrasonically cleaned with acetone and deionized water in turn; and finally, the substrate is blown dry.

[0058] In an embodiment of the present invention, the temperature of the heated substrate is 80-200°C, preferably 100-180°C, more preferably 120-160°C, and even more preferably 140-150°C.

[0059] In an embodiment of the present invention, the power sources of the MgF2 and ZnS targets are turned on, and ignition is simultaneously performed on the two cathode targets; MgF2 and ZnS are pre-sputtered first, and then the sample disk rotation speed is set, so that the substrate on the sample disk passes through the MgF2 and ZnS targets in sequence and faces the MgF2 and ZnS targets respectively, and finally the target baffle is opened to perform thin film deposition.

[0060] In an embodiment of the present invention, the sputtering power of the MgF2 target is 150-200W, preferably 160-190W, and more preferably 170-180W; the sputtering power of the ZnS target is 20-100W, preferably 30-80W, more preferably 40-70W, and even more preferably 50-60W.

[0061] In an embodiment of the present invention, the pre-sputtering time is 5 to 15 minutes, preferably 10 minutes.

[0062] In an embodiment of the present invention, the speed at which the substrate passes through the MgF2 target is 1 to 6 rpm, preferably 2 to 5 rpm, and more preferably 3 to 4 rpm; the speed at which the substrate passes through the ZnS target is 1 to 6 rpm, preferably 2 to 5 rpm, and more preferably 3 to 4 rpm.

[0063] In the embodiment of the present invention, after the deposition is completed, the substrate temperature is cooled to room temperature, and the sample is taken out, and the preparation of the MgF2-ZnS composite thin film is completed.

[0064] The present invention also provides a MgF2-ZnS composite film prepared by the above preparation method.

[0065] In an embodiment of the present invention, the refractive index of the MgF2-ZnS composite film is adjustable between 1.38 and 2.13.

[0066] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0067] Example 1

[0068] Step 1: Pre-treat the substrate

[0069] The double-sided polished Si substrate was first rinsed with deionized water to remove surface particles; then the substrate surface was wiped with absorbent cotton soaked in acetone and alcohol to remove organic pollutants such as grease on the surface; then the substrate was ultrasonically cleaned with acetone and deionized water in sequence; and finally, the substrate was blown dry.

[0070] Step 2: Prepare MgF2-ZnS composite film by sequential magnetron sputtering

[0071] The preparation process is as follows:

[0072] Step 2.1: Place the high-purity MgF2 target on a cathode target position (numbered 1#) in the vacuum chamber of the multi-target magnetron sputtering coating machine, and place the high-purity ZnS target on another cathode target position (numbered 2#). Place the pre-treated Si substrate on a sample tray perpendicular to the normal line of the MgF2 and ZnS target surfaces, and pump the background vacuum to <8×10 -4 Pa.

[0073] Step 2.2: Set the substrate heating temperature to 80°C; introduce Ar gas into the vacuum chamber with an Ar gas flow rate of 5 sccm and a vacuum chamber pressure of 0.1 Pa.

[0074] Step 2.3: Turn on the power sources for target #1 and target #2, and ignite simultaneously on both cathode targets; set the sputtering power of the MgF2 target to 150 W and the sputtering power of the ZnS target to 20 W; pre-sputter the MgF2 and ZnS for about 10 minutes, then set the sample stage speed so that the substrate passes through the MgF2 target and the ZnS target at a rate of 6 rpm. Finally, open the target baffle to deposit the thin film for 60 minutes.

[0075] Step 2.4: After the deposition is completed, wait for the substrate temperature to cool to room temperature and remove the sample. The performance of the sample is tested, and the results are as follows:

[0076] Figure 1This is a scanning electron micrograph (SEM) of a cross-section of a MgF2-ZnS composite film. It shows no obvious columnar crystal structure, a dense internal structure without pores or gaps, and a smooth, flat, and clean surface. Atomic force microscopy (AFM) testing reveals a surface roughness of 0.36 nm. Figure 2 It is a narrow scan spectrum of Mg, F, Zn and S measured by X-ray photoelectron spectrometer (XPS). It can be seen that Mg-F and Zn-S chemical bonds are formed in the MgF2-ZnS composite film, and it can be seen that no other substances except MgF2 and ZnS are formed; calculation shows that the atomic percentages of Mg, F, Zn and S in the composite film are 28.47, 56.65, 7.47 and 7.41 respectively, Mg:F is 1:1.98, Zn:S is 1:1, and the ratio of MgF2 to ZnS is 3.8:1. Figure 3 The n and k curves of the MgF2-ZnS composite film in the 2-12 μm band tested by ellipsometry are shown in Figure 1. The refractive index at a wavelength of 10 μm is n = 1.66 (see Figure 19 midpoint). Figure 4 This is the water contact angle test result of the composite film. It can be seen that the water contact angle is 105.0°, which is hydrophobic.

[0077] Example 2

[0078] Step 1: Pre-treat the substrate

[0079] The double-sided polished glass substrate is first rinsed with deionized water to remove surface particles; then the substrate surface is wiped with absorbent cotton soaked in acetone and alcohol to remove organic pollutants such as grease on the surface; then the substrate is ultrasonically cleaned with acetone and deionized water in sequence; finally, the substrate is blown dry.

[0080] Step 2: Prepare MgF2-ZnS composite film by sequential magnetron sputtering

[0081] The preparation process is as follows:

[0082] Step 2.1: Place the high-purity MgF2 target on a cathode target position (numbered 1#) in the vacuum chamber of the multi-target magnetron sputtering coating machine, and place the high-purity ZnS target on another cathode target position (numbered 2#). Place the pre-treated glass substrate on the sample tray perpendicular to the normal line of the MgF2 and ZnS target surfaces, and pump the background vacuum to <8×10 -4 Pa.

[0083] Step 2.2: Set the substrate heating temperature to 100°C; introduce Ar gas into the vacuum chamber with an Ar gas flow rate of 7 sccm and a vacuum chamber pressure of 0.2 Pa.

[0084] Step 2.3: Turn on the power sources for target #1 and target #2, and ignite simultaneously on both cathode targets. Set the sputtering power of the MgF2 target to 170 W and the sputtering power of the ZnS target to 20 W. Pre-sputter the MgF2 and ZnS for about 10 minutes, then set the sample stage speed so that the substrate passes through the MgF2 target and the ZnS target at 4 rpm. Finally, open the target baffle to deposit the thin film for 40 minutes.

[0085] Step 2.4: After the deposition is completed, wait for the substrate temperature to cool to room temperature and remove the sample. The performance of the sample is tested, and the results are as follows:

[0086] Figure 5 This is an AFM photograph of the MgF2-ZnS composite film we prepared. It can be seen that the surface of the composite film is dense, smooth, flat and clean. The surface roughness of the composite film is measured to be 0.42 nm. Figure 6 This is a SEM cross-sectional photograph of the MgF2-ZnS composite film we prepared. It can be seen that the composite film does not have an obvious columnar crystal structure, and the internal structure is dense without holes or gaps. Figure 7 This is the XPS full scan spectrum of the composite film we prepared. It can be seen that the peaks of F and Mg in the composite film are very strong, the peaks of Zn and S are very weak, and no peaks of other elements appear. Therefore, the composite film mainly contains F and Mg, and the content of Zn and S is very small, and no other impurities appear. The XPS narrow scan spectrum test results show that Mg-F and Zn-S chemical bonds are formed in the MgF2-ZnS composite film. It can be seen that no other substances except MgF2 and ZnS are formed; it can be calculated that the atomic percentages of Mg, F, Zn, and S in the composite film are 32.91, 65.02, 1.09, and 0.99, respectively, Mg:F is 1:1.97, Zn:S is 1.1:1, and the ratio of MgF2 to ZnS is 30:1. The test results of the ellipsometry spectrometer show that the refractive index of the composite film at a wavelength of 10μm is n=1.47 (see Figure 19 The water contact angle test results show that the composite film has a water contact angle of 103.9°, which is hydrophobic.

[0087] Example 3

[0088] Step 1: Pre-treat the substrate

[0089] The double-sided polished multi-spectral ZnS substrate was first rinsed with deionized water to remove surface particles; then the substrate surface was wiped with absorbent cotton soaked in acetone and alcohol to remove organic pollutants such as grease on the surface; then the substrate was ultrasonically cleaned with acetone and deionized water in sequence; and finally, the substrate was blown dry.

[0090] Step 2: Prepare MgF2-ZnS composite film by sequential magnetron sputtering

[0091] The preparation process is as follows:

[0092] Step 2.1: Place the high-purity MgF2 target on a cathode target position (numbered 1#) in the vacuum chamber of the multi-target magnetron sputtering coating machine, and place the high-purity ZnS target on another cathode target position (numbered 2#). Place the pre-treated ZnS substrate on a sample tray perpendicular to the normal line of the MgF2 and ZnS target surfaces, and pump the background vacuum to <8×10 -4 Pa.

[0093] Step 2.2: Set the substrate heating temperature to 120°C; introduce Ar gas into the vacuum chamber with an Ar gas flow rate of 10 sccm and a vacuum chamber pressure of 0.3 Pa.

[0094] Step 2.3: Turn on the power sources for target #1 and target #2, and ignite simultaneously on both cathode targets. Set the sputtering power of the MgF2 target to 200W and the sputtering power of the ZnS target to 20W. Pre-sputter the MgF2 and ZnS for about 10 minutes, then set the sample stage speed so that the substrate passes through the MgF2 target and the ZnS target at a rate of 2 rpm. Finally, open the target baffle to deposit the thin film for 40 minutes.

[0095] Step 2.4: After the deposition is completed, wait for the substrate temperature to cool to room temperature and remove the sample. The performance of the sample is tested, and the results are as follows:

[0096] Figure 8 This is the surface SEM image of the MgF2-ZnS composite film we prepared. It can be seen that the surface of the composite film is smooth, flat and clean. AFM observation test shows that the surface roughness of the composite film is 0.389nm. The cross-sectional SEM observation results show that the film does not have an obvious columnar crystal structure, the internal structure is dense, and there are no holes or gaps. The XPS narrow scan spectrum test results show that Mg-F and Zn-S chemical bonds are formed in the MgF2ZnS composite film, and it can be seen that no other substances except MgF2 and ZnS are formed; the calculated atomic percentages of Mg, F, Zn, and S in the composite film are 33.4826, 66.1714, 0.1829, and 0.16308, respectively, Mg:F is 1:1.98, Zn:S is 1.1:1, and the ratio of MgF2 to ZnS is 185:1. The ellipsometry test results show that the refractive index of the composite film at a wavelength of 10μm is n=1.383 (see Figure 19 The water contact angle test results show that the composite film has a water contact angle of 102.5°, which is hydrophobic.

[0097] Example 4

[0098] Step 1: Pre-treat the substrate

[0099] The double-sided polished Si substrate was first rinsed with deionized water to remove surface particles; then the substrate surface was wiped with absorbent cotton soaked in acetone and alcohol to remove organic pollutants such as grease on the surface; then the substrate was ultrasonically cleaned with acetone and deionized water in sequence; and finally, the substrate was blown dry.

[0100] Step 2: Prepare MgF2-ZnS composite film by sequential magnetron sputtering

[0101] The preparation process is as follows:

[0102] Step 2.1: Place the high-purity MgF2 target on a cathode target position (numbered 1#) in the vacuum chamber of the multi-target magnetron sputtering coating machine, and place the high-purity ZnS target on another cathode target position (numbered 2#). Place the pre-treated Si substrate on a sample tray perpendicular to the normal line of the MgF2 and ZnS target surfaces, and pump the background vacuum to <8×10 -4 Pa.

[0103] Step 2.2: Set the substrate heating temperature to 140°C; introduce Ar gas into the vacuum chamber with an Ar gas flow rate of 5 sccm and a vacuum chamber pressure of 0.1 Pa.

[0104] Step 2.3: Turn on the power sources for target #1 and target #2, and ignite simultaneously on both cathode targets; set the sputtering power of the MgF2 target to 150 W and the sputtering power of the ZnS target to 40 W; pre-sputter the MgF2 and ZnS for about 10 minutes, then set the sample stage speed so that the substrate passes through the MgF2 target and the ZnS target at a rate of 5 rpm. Finally, open the target baffle to deposit the thin film for 50 minutes.

[0105] Step 2.4: After the deposition is completed, wait for the substrate temperature to cool to room temperature and remove the sample. The performance of the sample is tested, and the results are as follows:

[0106] Figure 9This is a cross-sectional SEM image of the MgF2-ZnS composite film we prepared. It can be seen that the composite film does not have an obvious columnar crystal structure, the internal structure is dense, there are no holes or gaps, and the surface is smooth and flat. AFM observation test shows that the surface roughness of the composite film is 0.465nm. XPS narrow scan spectrum test results show that the MgF2-ZnS composite film forms Mg-F and Zn-S chemical bonds, and it can be seen that no other substances except MgF2 and ZnS are formed; calculations show that the atomic percentages of Mg, F, Zn, and S in the composite film are 20.1221, 39.7369, 20.294, and 19.847, respectively, Mg:F is 1:1.97, Zn:S is 1:1, and the ratio of MgF2 to ZnS is 1:1. The results of the ellipsometry test show that the refractive index of the composite film at a wavelength of 10μm is n=1.73 (see Figure 19 The water contact angle test results show that the composite film has a water contact angle of 104.5°, which is hydrophobic.

[0107] Example 5

[0108] Step 1: Pre-treat the substrate

[0109] The double-sided polished glass substrate is first rinsed with deionized water to remove surface particles; then the substrate surface is wiped with absorbent cotton soaked in acetone and alcohol to remove organic pollutants such as grease on the surface; then the substrate is ultrasonically cleaned with acetone and deionized water in sequence; finally, the substrate is blown dry.

[0110] Step 2: Prepare MgF2-ZnS composite film by sequential magnetron sputtering

[0111] The preparation process is as follows:

[0112] Step 2.1: Place the high-purity MgF2 target on a cathode target position (numbered 1#) in the vacuum chamber of the multi-target magnetron sputtering coating machine, and place the high-purity ZnS target on another cathode target position (numbered 2#). Place the pre-treated glass substrate on the sample tray perpendicular to the normal line of the MgF2 and ZnS target surfaces, and pump the background vacuum to <8×10 -4 Pa.

[0113] Step 2.2: Set the substrate heating temperature to 170°C; introduce Ar gas into the vacuum chamber with an Ar gas flow rate of 7 sccm and a vacuum chamber pressure of 0.2 Pa.

[0114] Step 2.3: Turn on the power sources for target #1 and target #2, and ignite simultaneously on both cathode targets; set the sputtering power of the MgF2 target to 150 W and the sputtering power of the ZnS target to 80 W; pre-sputter the MgF2 and ZnS for about 10 minutes, then set the sample stage speed so that the substrate passes through the MgF2 target and the ZnS target at a rate of 3 rpm. Finally, open the target baffle to deposit the thin film for 40 minutes.

[0115] Step 2.4: After the deposition is completed, wait for the substrate temperature to cool to room temperature and remove the sample. The performance of the sample is tested, and the results are as follows:

[0116] Figure 10 This is the surface AFM photograph of the MgF2-ZnS composite film we prepared. It can be seen that the surface of the composite film is dense, smooth, flat and clean. The surface roughness of the composite film is measured to be 0.55 nm. Figure 11 This is the XPS full scan spectrum of the MgF2-ZnS composite film we prepared. It can be seen that the peaks of F, Mg, Zn, and S in the composite film are relatively strong, and no peaks of other elements appear. Therefore, the composite film mainly contains F, Mg, Zn, and S, and no other impurities appear. The XPS narrow scan spectrum test results show that Mg-F and Zn-S chemical bonds are formed in the MgF2-ZnS composite film. It can be seen that no other substances except MgF2 and ZnS are formed; it can be calculated that the atomic percentages of Mg, F, Zn, and S in the composite film are 14.3697, 27.8683, 29.6477, and 28.1143, respectively. The Mg:F ratio is 1:1.93, the Zn:S ratio is 1.05:1, and the ratio of MgF2 to ZnS is 1:2. The ellipsometry test results show that the refractive index of the composite film at a wavelength of 10μm is n=1.89 (see Figure 19 The water contact angle test results show that the composite film has a water contact angle of 103.6°, which is hydrophobic.

[0117] Example 6

[0118] Step 1: Pre-treat the substrate

[0119] The double-sided polished multi-spectral ZnS substrate was first rinsed with deionized water to remove surface particles; then the substrate surface was wiped with absorbent cotton soaked in acetone and alcohol to remove organic pollutants such as grease on the surface; then the substrate was ultrasonically cleaned with acetone and deionized water in sequence; and finally, the substrate was blown dry.

[0120] Step 2: Prepare MgF2-ZnS composite film by sequential magnetron sputtering

[0121] The preparation process is as follows:

[0122] Step 2.1: Place the high-purity MgF2 target on a cathode target position (numbered 1#) in the vacuum chamber of the multi-target magnetron sputtering coating machine, and place the high-purity ZnS target on another cathode target position (numbered 2#). Place the pre-treated ZnS substrate on a sample tray perpendicular to the normal line of the MgF2 and ZnS target surfaces, and pump the background vacuum to <8×10 -4 Pa.

[0123] Step 2.2: Set the substrate heating temperature to 200°C; introduce Ar gas into the vacuum chamber with an Ar gas flow rate of 10 sccm and a vacuum chamber pressure of 0.3 Pa.

[0124] Step 2.3: Turn on the power sources for target #1 and target #2, and ignite simultaneously on both cathode targets. Set the sputtering power of the MgF2 target to 150 W and the sputtering power of the ZnS target to 100 W. Pre-sputter the MgF2 and ZnS for about 10 minutes, then set the sample stage speed so that the substrate passes through the MgF2 target and the ZnS target at a rate of 1 rpm. Finally, open the target baffle to deposit the thin film for 30 minutes.

[0125] Step 2.4: After the deposition is completed, wait for the substrate temperature to cool to room temperature and remove the sample. The performance of the sample is tested, and the results are as follows:

[0126] Figure 12 This is the surface AFM photograph of the MgF2-ZnS composite film we prepared. It can be seen that the surface of the composite film is dense, smooth, flat and clean. The surface roughness of the composite film is measured to be 0.62nm. The XPS narrow scan spectrum test results show that Mg-F and Zn-S chemical bonds are formed in the MgF2-ZnS composite film. It can be seen that no other substances except MgF2 and ZnS are formed; the calculated atomic percentages of Mg, F, Zn and S in the composite film are 6.73, 13.35, 40.31 and 39.61 respectively, Mg:F is 1:1.98, Zn:S is 1:1, and the ratio of MgF2 to ZnS is 1:6. The ellipsometry test results show that the refractive index of the composite film at a wavelength of 10μm is n=2.13 (see Figure 19 The water contact angle test results show that the composite film has a water contact angle of 102.2°, which is hydrophobic.

[0127] Example 7

[0128] Step 1: Pre-treat the substrate

[0129] The double-sided polished Si substrate was first rinsed with deionized water to remove surface particles; then the substrate surface was wiped with absorbent cotton soaked in acetone and alcohol to remove organic pollutants such as grease on the surface; then the substrate was ultrasonically cleaned with acetone and deionized water in sequence; and finally, the substrate was blown dry.

[0130] Step 2: Prepare MgF2-ZnS composite film by sequential magnetron sputtering

[0131] The preparation process is as follows:

[0132] Step 2.1: Place the high-purity MgF2 target on a cathode target position (numbered 1#) in the vacuum chamber of the multi-target magnetron sputtering coating machine, and place the high-purity ZnS target on another cathode target position (numbered 2#). Place the pre-treated Si substrate on a sample tray perpendicular to the normal line of the MgF2 and ZnS target surfaces, and pump the background vacuum to <8×10 -4 Pa.

[0133] Step 2.2: Set the substrate heating temperature to 100°C; introduce Ar gas into the vacuum chamber with an Ar gas flow rate of 10 sccm and a vacuum chamber pressure of 0.3 Pa.

[0134] Step 2.3: Turn on the power sources for target #1 and target #2, and ignite simultaneously on both cathode targets; set the sputtering power of the MgF2 target to 200W and the sputtering power of the ZnS target to 100W; pre-sputter the MgF2 and ZnS for about 10 minutes, then set the sample stage speed so that the substrate passes through the MgF2 target at a rate of 2 rpm and the ZnS target at a rate of 4 rpm. Finally, open the target baffle to deposit the thin film for 50 minutes.

[0135] Step 2.4: After the deposition is completed, wait for the substrate temperature to cool to room temperature and remove the sample. The performance of the sample is tested, and the results are as follows:

[0136] Figure 13 This is a surface SEM photo of the MgF2-ZnS composite film we prepared. It can be seen that the surface of the composite film is dense, smooth, flat, and clean. AFM observation test results show that the surface roughness of the composite film is 0.325nm. Figure 14This is the full-scan XPS spectrum of the MgF2-ZnS composite film we prepared. It can be seen that the peaks for F, Mg, Zn, and S are all strong in the composite film, with no peaks for other elements present. Therefore, the composite film primarily contains F, Mg, Zn, and S, with no other impurities present. The XPS narrow-scan spectrum test results indicate the formation of Mg-F and Zn-S chemical bonds in the MgF2-ZnS composite film, indicating the absence of other species besides MgF2 and ZnS. Calculated atomic percentages of Mg, F, Zn, and S in the composite film are 25.8373, 50.9835, 11.9649, and 11.2143, respectively. The Mg:F ratio is 1:1.97, the Zn:S ratio is 1.06:1, and the MgF2:ZnS ratio is 2.16:1. Figure 15 The n and k curves of the composite film in the 2-12 μm band tested by ellipsometry are shown in Figure 1. The refractive index at a wavelength of 10 μm is n = 1.7 (see Figure 19 The water contact angle test results show that the composite film has a water contact angle of 103.7°, which is hydrophobic.

[0137] Example 8

[0138] Step 1: Pre-treat the substrate

[0139] The double-sided polished Si substrate was first rinsed with deionized water to remove surface particles; then the substrate surface was wiped with absorbent cotton soaked in acetone and alcohol to remove organic pollutants such as grease on the surface; then the substrate was ultrasonically cleaned with acetone and deionized water in sequence; and finally, the substrate was blown dry.

[0140] Step 2: Prepare MgF2-ZnS composite film by sequential magnetron sputtering

[0141] The preparation process is as follows:

[0142] Step 2.1: Place the high-purity MgF2 target on a cathode target position (numbered 1#) in the vacuum chamber of the multi-target magnetron sputtering coating machine, and place the high-purity ZnS target on another cathode target position (numbered 2#). Place the pre-treated Si substrate on a sample tray perpendicular to the normal line of the MgF2 and ZnS target surfaces, and pump the background vacuum to <8×10 -4 Pa.

[0143] Step 2.2: Set the substrate heating temperature to 200°C; introduce Ar gas into the vacuum chamber with an Ar gas flow rate of 5 sccm and a vacuum chamber pressure of 0.1 Pa.

[0144] Step 2.3: Turn on the power sources for target #1 and target #2, and ignite simultaneously on both cathode targets; set the sputtering power of the MgF2 target to 200W and the sputtering power of the ZnS target to 100W; pre-sputter the MgF2 and ZnS for about 10 minutes, then set the sample stage speed so that the substrate passes through the MgF2 target at a rate of 3 rpm and the ZnS target at a rate of 1 rpm. Finally, open the target baffle to deposit the thin film for 60 minutes.

[0145] Step 2.4: After the deposition is completed, wait for the substrate temperature to cool to room temperature and remove the sample. The performance of the sample is tested, and the results are as follows:

[0146] The results of SEM and AFM observations show that the surface of the composite film is dense, smooth, flat and clean, with a surface roughness of 0.48 nm. Figure 16 This is the full-scan XPS spectrum of the MgF2-ZnS composite film we prepared. It can be seen that the peaks for F, Mg, Zn, and S are all strong in the composite film, with no peaks for other elements present. Therefore, the composite film primarily contains F, Mg, Zn, and S, with no other impurities present. The XPS narrow-scan spectrum test results indicate the formation of Mg-F and Zn-S chemical bonds in the MgF2-ZnS composite film, indicating the absence of other species besides MgF2 and ZnS. Calculated atomic percentages of Mg, F, Zn, and S in the composite film are 10.4689, 20.7104, 34.7998, and 34.0209, respectively. The Mg:F ratio is 1:1.98, the Zn:S ratio is 1.02:1, and the MgF2:ZnS ratio is 1:3.3. Figure 17 The n and k curves of the MgF2-ZnS composite film in the 2-12 μm band are shown. The refractive index is 1.96 at a wavelength of 10 μm (see Figure 19 midpoint). Figure 18 This is the water contact angle of the MgF2-ZnS composite film we prepared. It can be seen that the water contact angle is 104.9°, which is hydrophobic.

[0147] The present invention further deposits other MgF2-ZnS composite films with different MgF2 and ZnS content ratios through process control, thereby realizing MgF2-ZnS composite films with more refractive index changes. Figure 19 The variation of the refractive index (n) of the MgF2-ZnS composite film at a wavelength of 10 μm with the content ratio of MgF2 and ZnS is given. It can be seen that by adjusting the content ratio of MgF2 and ZnS, the refractive index of the MgF2-ZnS composite film can be continuously varied in the range of 1.38 to 2.13.

[0148] In summary, the embodiments of the present invention are based on MgF2 (n = 1.37) and ZnS (n = 2.2) and magnetron sputtering technology to develop a sequential sputtering method for preparing MgF2-ZnS composite films. By adjusting the process parameters, the content ratio of MgF2 and ZnS in the composite film can be changed, and the atomic ratios of Mg:F and Zn:S in the composite film are close to the stoichiometric ratios of 1:2 and 1:1, respectively, thereby achieving continuous adjustment of the infrared refractive index at a lower refractive index and in a wider range (n = 1.38 to 2.13).

[0149] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a MgF2-ZnS composite film, characterized in that: The following steps are involved: 1) MgF2 and ZnS are used as target materials, installed on two different cathodes respectively, and sputtered simultaneously on the MgF2 target and the ZnS target under vacuum conditions; 2) Place the substrate on a sample tray perpendicular to the normal lines of the MgF2 target and the ZnS target surface, rotate the sample tray, and allow the substrate on the sample tray to pass through the MgF2 and ZnS targets in sequence and face the MgF2 and ZnS targets respectively, thereby sequentially depositing MgF2 and ZnS on the substrate to form a MgF2-ZnS composite film; The sputtering gas is argon, and the vacuum condition is a vacuum degree of <8×10 -4 Pa.

2. The preparation method according to claim 1, characterized in that The flow rate of the argon gas is 5-10 sccm.

3. The preparation method according to claim 1, characterized in that The sputtering gas pressure is 0.1-0.3 Pa.

4. The preparation method according to claim 1, characterized in that The sputtering power of the MgF2 target is 150-200W; the sputtering power of the ZnS target is 20-100W.

5. The preparation method according to claim 1, characterized in that The temperature of the substrate is 80-200°C.

6. The preparation method according to claim 1, characterized in that The speed at which the substrate passes through the MgF2 target is 1 to 6 rpm; the speed at which the substrate passes through the ZnS target is 1 to 6 rpm.

7. A MgF2-ZnS composite thin film prepared by the preparation method according to any one of claims 1 to 6.

8. The MgF2-ZnS composite film according to claim 7, characterized in that The refractive index of the MgF2-ZnS composite film is adjustable between 1.38 and 2.13.

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