JP2014148718A - Method for producing hydroxyapatite thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To readily produce a thin film of hydroxyapatite a surface of which has a C face.SOLUTION: In a first process S101, a thin film 102 is formed on a sapphire substrate 101 having a main surface with a C face by using an electron cyclotron resonance (ECR) sputtering method using a target composed of a sintered body of hydroxyapatite and xenon gas including HO gas (first process). Then, the thin film 102 (sapphire substrate 101) is heated in the atmosphere having oxygen for crystallization (second process). It may be done in the atmosphere of oxygen gas or in the ambient air.

Description

  The present invention relates to a method for producing a hydroxyapatite thin film that forms a hydroxyapatite thin film having a C-face surface.

Hydroxyapatite [Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ ] is a main component constituting bones and teeth, and is an artificially synthesized biocompatible inorganic material that can be used for medical engineering and biotechnology. Applied to technology. In particular, it has been pointed out that by controlling the properties of hydroxyapatite films formed on various substrates, it is possible to pioneer new applications while prescribing interactions with biological materials. For example, a hydroxyapatite crystal film terminated at the C-plane has a structure similar to bone and can be used as a platform in studying the interaction between bone and biological material.

  At present, hydroxyapatite is used in the field of medical biology as a scaffold material for cell culture. For example, a hydroxyapatite porous material or paste is embedded in a bone defect to promote bone regeneration. When a hydroxyapatite thin film deposited on a substrate is used for the intermediate layer instead of these powders and pastes, it is expected that the joint strength with the bone will be higher and a treatment with quick recovery will be possible. In addition, the surface of a metal structure embedded in a living body is used by being coated with a hydroxyapatite film.

  As is apparent from the above, a technique for forming a hydroxyapatite film on various substrates (substrates) is important. For example, when the surface of a metal structure is covered with a hydroxyapatite film, it is mainly performed by a plasma spray method. In addition, various attempts have been made to form a hydroxyapatite film on a substrate so far. For example, the formation of a hydroxyapatite film by RF magnetron sputtering (see Non-Patent Documents 1 and 2), the formation of a hydroxyapatite film by ion beam sputtering (see Non-Patent Document 3), and the formation of a hydroxyapatite film by pulsed laser deposition (PLD) method Formation (see Non-Patent Document 4) has been reported.

K. Yamashita, T. Arashi, K. Kitagaki, S. Yamada, and T. Umegaki, "Preparation of Apatite Thin Films through rf-Sputtering form Calcium Phosphate Glasses", J. Am. Ceram. Soc., Vol. 77. no.9, pp.2401-2407, 1994. K.van Dijk et al., "Influence of annealing temperature on RF magnetron aputtered calcium phosphate coatings", Biometerials, vol.17, pp.405-410, 1996. M. Hamdi and A. Ide-Ektessabi, "Preparation of hydroapatite layer by ion beam assisted simultaneous vapor deposition", Surface and Coatings Technology, 163-164, pp.362-367, 2003. JM Fernandez-Pradas, G. Sardin, L. Cleries, P. Serra, C. Ferrater, and JL Morenza, "Deposition of hydroxyapatite thin films by excimer laser ablation", Thin Solid Films, vol.317, pp393-396, 1998 .

  However, the crystal orientation of the hydroxyapatite film formed by the above-described technique is usually random orientation. On the other hand, a process technique for forming a hydroxyapatite film by precisely controlling the film thickness, composition, crystallinity, orientation, and the like is desired. In particular, the orientation is an important index that defines the interaction between the hydroxyapatite crystal thin film and other molecules. Hydroxyapatite crystal belongs to the hexagonal system, and the end face of the hexagonal column is constituted by the C plane and the side face is constituted by the A plane. The C surface is hydrophobic and the A surface is hydrophilic. Thus, the interaction with external molecules strongly depends on the plane index.

  For example, a bone is a structure in which a number of c-axis oriented hydroxyapatite nanocrystals of collagen fibers are arranged. Therefore, if a hydroxyapatite crystal film terminated with a C-plane is obtained, it is considered that research on the interaction between a bone-like hydroxyapatite crystal film and a biological material will gain momentum. It is also possible to develop a biosensor / biochip that uses the reactivity specific to the C-plane.

  However, as described above, the hydroxyapatite crystal film obtained by a general film forming method is basically randomly oriented, and has both hydrophilic and hydrophobic crystal faces. If the film forming conditions are appropriately selected, a crystal film having a main C-plane may be obtained. However, in this case, there is a problem that the range of process parameters is very narrow.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to facilitate the formation of a hydroxyapatite thin film having a C-face surface.

The method for producing a hydroxyapatite thin film according to the present invention is an electron cyclotron resonance sputtering method using a target made of a sintered hydroxyapatite and a xenon gas containing H ₂ O gas. A first step of forming a thin film thereon, and a second step of crystallizing the thin film by heating in an atmosphere in which oxygen is present.

  In the method for producing a hydroxyapatite thin film, in the second step, heating may be performed in the range of 600 ° C to 900 ° C.

  As described above, according to the present invention, it is possible to obtain an excellent effect that a hydroxyapatite thin film having a C-plane surface can be easily formed.

FIG. 1 is an explanatory diagram for explaining a method for producing a hydroxyapatite thin film according to an embodiment of the present invention. FIG. 2 is a configuration diagram showing the configuration of the ECR sputtering apparatus. FIG. 3 is a characteristic diagram showing an X-ray diffraction pattern of a hydroxyapatite thin film produced by the production method according to the embodiment of the present invention. FIG. 4 is a characteristic diagram showing an X-ray diffraction pattern of a sample grown using xenon gas and maintaining a sapphire substrate having a C-plane main surface at 420 ° C. or 470 ° C. while crystallizing the deposited hydroxyapatite film. is there. FIG. 5 is a characteristic diagram showing an X-ray diffraction pattern of a hydroxyapatite film formed without being c-axis oriented. FIG. 6 is a characteristic diagram showing the heating temperature dependence of the Raman spectrum of a hydroxyapatite film formed by ECR sputtering on a sapphire substrate having a C-plane main surface. FIG. 7 is a characteristic diagram showing the heating temperature dependence of the Raman spectrum of a hydroxyapatite film formed by ECR sputtering on a sapphire substrate whose main surface is an A-plane. FIG. 8 is a characteristic diagram showing the relationship between the heating temperature of the formed hydroxyapatite film and the contact angle of water in each of the sapphire substrate having the main surface as the C-plane and the sapphire substrate having the main surface as the A-plane. is there.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram for explaining a method for producing a hydroxyapatite thin film according to an embodiment of the present invention. This manufacturing method is an electron cyclotron resonance (ECR) sputtering method using a sputtering gas containing a target composed of a sintered body of hydroxyapatite and H ₂ O gas in the first step S101. (Corundum) A hydroxyapatite thin film 102 is formed on a substrate 101 (first step). The sputtering gas is xenon gas.

For example, the pressure of the H ₂ O gas may be set in the range of 10 ⁻³ Pa to 10 ⁻² Pa. The microwave power for generating ECR plasma may be 500 W, and the RF power applied to the target may be 500 W.

  Next, the thin film 102 is heated and crystallized in an atmosphere in which oxygen is present (second step). For example, the thin film 102 may be heated by heating the sapphire substrate 101 over which the thin film 102 is formed in an oxygen gas atmosphere or in the air.

As described above, by using the ECR sputtering method, it is possible to form a film under a gas pressure as low as 10 ⁻² Pa, and it has been demonstrated for many materials that a high-quality thin film can be obtained. The ECR plasma is a remote plasma, and when combined with a cylindrical target, the plasma damage to the thin film due to anion incidence is small.

  In addition, although the film formation rate of the ECR sputtering method is not so high, since the film formation time is required, the time during which the plasma is irradiated during the film formation is long. For example, during film formation, low energy ions of 10-30 eV are continuously irradiated on the thin film. As a result, the plasma promotes atomic diffusion between the hydroxyapatite thin film and the substrate, and the greatest feature is that excellent adhesion can be obtained without interposing an adhesive layer between the substrate and the hydroxyapatite thin film. doing. This is an advantage not found in other sputtering methods or PLD methods. Furthermore, an apparatus that realizes the ECR sputtering method can form a large area film up to an 8-inch substrate, which is impossible with the PLD method, and is suitable for production purposes.

In addition, since a sputtering gas containing H ₂ O gas is used, OH can be efficiently taken into the formed thin film as described below, and a high-quality hydroxyapatite thin film is formed. it can. Hydroxyapatite contains an OH group as a constituent element. However, when a hydroxyapatite target is sputtered, OH having a small mass is scattered in a wide range, and all of these do not reach the substrate. For this reason, it is necessary to supplement the OH groups incorporated into the thin film. When a mixed gas of H ₂ and O ₂ gas is used, it is necessary to decompose H ₂ and O ₂ , and the flow rate ratio between them must be controlled. On the other hand, H ₂ O molecules are excellent as a reactive gas for supplementing OH to be taken into the deposited film because they generate OH groups immediately by being decomposed into OH and H.

As described above, the embodiment is characterized in that a sapphire substrate having a C-plane main surface is used. Here, the crystal unit unit of hydroxyapatite includes Ca ²⁺ , PO ₄ ³⁻ , OH ⁻ and three kinds of ions, and has a complicated structure. For this reason, unlike simple binary metal oxides, the atomic arrangement of the substrate hardly affects the atomic arrangement of the hydroxyapatite thin film formed on the substrate, and the C-plane terminal It is quite difficult to obtain a hydroxyapatite film. This means that depending on the growth conditions, a plane index plane different from the C plane may become a trend.

In contrast, in the present invention, as described above, in the present invention, using an ECR sputtering apparatus equipped with a hydroxyapatite sintered compact target, while flowing H ₂ O gas, at room temperature (20 to 25 ° C.), A first step of forming a hydroxyapatite film on a sapphire substrate having a main surface as a C-plane, and a second step of heating and crystallizing the hydroxyapatite film thus formed in an atmosphere containing oxygen gas Through this process, a hydroxyapatite film terminated only on the C-plane was obtained.

  In the ECR sputtering method, since remote plasma is sputtered by colliding with the RF applied target located downstream, as described above, there is little damage to the deposited film by the plasma, and excellent adhesion can be obtained. The feature is that large area film formation is possible. Further, as will be described later, the compositional deviation can be minimized by using xenon as the sputtering gas. Further, by setting the temperature (substrate temperature) at the time of heating in the second step to 600 ° C. or more and 900 ° C. or less, the formation of crystallites at the other position is suppressed, and the hydroxyapatite film terminated only on the C plane can get.

  Next, the hydroxyapatite thin film (sample) actually produced using the ECR sputtering method will be described together with the configuration of the ECR sputtering apparatus.

  As shown in FIG. 2, the ECR sputtering apparatus includes a film formation chamber 201 and a plasma generation chamber 203 that communicates with the film formation chamber 201. For example, 2.45 GHz microwaves can be supplied to the plasma generation chamber 203 by a microwave supply source 204. Further, around the plasma generation chamber 203, for example, a magnetic coil 205 that generates a magnetic field of 0.0875 T (Tesla) in the plasma generation chamber 203 is provided.

  In the film forming chamber 201, a ring-shaped target 202 surrounding the vicinity of the outlet of the plasma generation chamber 203 is disposed. The target 202 is made of, for example, a sintered body obtained by sintering hydroxyapatite powder, and a predetermined target bias (high frequency power) can be applied. Further, the sapphire substrate 101 placed in the film formation chamber 201 can be heated by a heater 206.

After the sapphire substrate 101 is placed at a predetermined distance from the target 202 in the film forming chamber 201 of the ECR sputtering apparatus configured as described above, a well-known exhaust mechanism (not shown) is used to perform the formation. The inside of the film chamber 201 is evacuated to a predetermined pressure. For example, the inside of the film forming chamber 201 is depressurized to a high vacuum state pressure of 10 ⁻⁴ to 10 ⁻⁵ Pa.

Next, xenon is introduced into a processing chamber of the ECR sputtering apparatus, for example, the plasma generation chamber 203 to obtain a predetermined degree of vacuum (pressure), and in this state, 2.45 GHz microwave (about 500 W) is generated by the magnetic coil 205. An ECR plasma is formed in the plasma generation chamber 203 by supplying a 0.0875 T magnetic field and setting the electron cyclotron resonance condition. In this state, H ₂ O gas is introduced into the film forming chamber 201 through a variable leak valve (not shown). The internal pressure was set to a level of 10 ⁻³ Pa to 10 ⁻² Pa by introducing H ₂ O gas.

The ECR plasma generated as described above is emitted from the plasma generation chamber 203 to the film formation chamber 201 connected to the plasma generation chamber 203 by the divergent magnetic field of the magnetic coil of the ECR sputtering apparatus. In this state, for example, high frequency power (target bias) of 13.56 MHz · 500 W is supplied (applied) to the target 202 disposed at the outlet of the plasma generation chamber 203. As a result, the particles generated by the generated ECR plasma collide with the target 202 to cause a sputtering phenomenon, and the particles constituting the target 202 jump out. Further, OH and H are generated from H ₂ O introduced into the film formation chamber 201.

By generating ECR plasma in the sputter state as described above, particles sputtered from the target 202 are deposited on the sapphire substrate 101, and a thin film 102 (hydroxyapatite thin film) is formed on the sapphire substrate 101. Is formed. In addition, OH and H are taken into a film deposited on the sapphire substrate 101. Note that the sapphire substrate 101 was not heated during the film formation, but the substrate temperature rose to about 70 ° C. by the plasma irradiation. A hydroxyapatite thin film having a film thickness of 0.8-1 μm was formed, although it varied somewhat depending on the H ₂ O gas pressure during film formation.

Heating for crystallization is performed in an oxygen atmosphere and in the air. Further, a plurality of samples are manufactured by changing the H ₂ O gas partial pressure during film formation and the heating temperature for crystallization. For comparison, a comparative sample heated in vacuum, a comparative sample heated during film formation, and a comparative sample prepared using argon gas as a sputtering gas were also prepared. For comparison, a comparative sample in which a hydroxyapatite thin film was formed on a sapphire substrate having the main surface as the A plane as described above was also produced. Note that heating may be performed by the heater 206 inside the deposition chamber 201. For example, if oxygen is introduced into the deposition chamber 201 without generating plasma, heating in an oxygen atmosphere can be performed. The formed thin film had a smooth surface and did not crack or peel off under any film forming / heating conditions.

FIG. 3 is a characteristic diagram showing an X-ray diffraction pattern of each sample using a hydroxyapatite thin film manufactured by the manufacturing method according to the above-described embodiment. Here, a hydroxyapatite thin film formed by an ECR sputtering method with a partial pressure of H ₂ O of 1.3 × 10 ⁻² Pa is subjected to temperature conditions of 500 ° C., 550 ° C., 600 ° C., 900 in an oxygen atmosphere. 2 shows an X-ray diffraction pattern of a hydroxyapatite thin film in a sample formed by heating (annealing) at ° C. In addition, an X-ray diffraction pattern of a hydroxyapatite thin film in a sample heated at a temperature condition of 900 ° C. in vacuum exhaust is also shown. 500 ° C. and 550 ° C. have a heating time of 10 hours, 600 ° C. has a heating time of 2 hours, and 900 ° C. has a heating time of 1 hour.

  Under the conditions of 500 ° C. and 550 ° C. (10 hours), it can be seen that the diffraction peak from the hydroxyapatite crystal is very weak and the crystallization has not progressed sufficiently. On the other hand, only the hydroxyapatite (002) and hydroxyapatite (004) peaks are strongly observed under the condition of 600 ° C., indicating that a hydroxyapatite film terminated at the C plane is obtained. Yes.

Further, the condition of 900 ° C. in an oxygen atmosphere should be sufficiently crystallized, but the hydroxyapatite (002) peak is rather low. This is because, when heated at a high temperature, H ₂ O molecules contained in the deposited amorphous hydroxyapatite film are thermally desorbed, and a sufficient amount of OH groups cannot be obtained for constituting a hydroxyapatite crystal. Conceivable. When heated at a temperature higher than 900 ° C., CA ₃ (PO ₄ ) ₂ (TCP) from which OH groups are completely removed is generated. Therefore, it is appropriate to consider that the upper limit of the heating temperature is 900 ° C.

  Moreover, about the comparative sample heated at 900 degreeC in the vacuum for 1 hour, a hydroxyapatite (002) peak is not seen at all, suggesting that OH group was lost.

  From the above experimental results, it can be said that it is appropriate to heat the hydroxyapatite film in a temperature range of 600 ° C. or higher and 900 ° C. or lower in oxygen gas.

  Next, the results of film formation under other conditions will be described with reference to FIG. Below, the case where deposition by sputtering is performed while heating the sapphire substrate will be described. FIG. 4 is a characteristic diagram showing an X-ray diffraction pattern of a comparative sample grown using a xenon gas and a sapphire substrate whose main surface is C-plane kept at 420 ° C. or 470 ° C. and crystallizing the deposited hydroxyapatite film. It is.

  Since the hydroxyapatite film was not sufficiently crystallized at a temperature of 400 ° C. or lower, 420 ° C. is a practical lower limit temperature for crystallization. As shown in FIG. 4, it can be seen that at 420 ° C., the hydroxyapatite (002) peak is preferentially oriented in the c-axis direction. On the other hand, when the substrate temperature was raised to 470 ° C., the hydroxyapatite (002) peak intensity decreased and the hydroxyapatite (310) peak became a trend.

  No X-ray diffraction pattern having the maximum hydroxyapatite (310) peak has been reported so far for any hydroxyapatite film formed on any substrate. Therefore, it is considered that the hydroxyapatite (310) plane also lattice-matched with the sapphire C plane and epitaxial growth occurred. From these results, in order to form a hydroxyapatite film terminated at the C-plane (the surface is the C-plane), the substrate temperature must be set to 420 ° C. without excess or deficiency, which is permitted. The process temperature range was found to be very narrow. Further, the intensity of the hydroxyapatite (002) peak is 500 counts and remains 1/3 compared to 1500 counts at 600 ° C. in FIG.

  Therefore, in the process of heating and crystallizing during film formation, the allowable range is narrow and crystallization is not so high, so it is better to perform solid phase epitaxial growth with heating after film formation. Advantageous membranes are obtained and are advantageous.

  Next, a case where a hydroxyapatite film that is not c-axis oriented is generated will be described. FIG. 5 is a characteristic diagram showing an X-ray diffraction pattern of a hydroxyapatite film formed without being c-axis oriented. In FIG. 5, “C-phase” indicates the result of a sample in which a hydroxyapatite film is formed on a sapphire substrate having a main surface as a C-plane, and “A-phase” indicates a sapphire substrate having a main surface as an A-plane. The result of a comparative sample having a hydroxyapatite film formed thereon is shown.

  For example, a hydroxyapatite film is formed at room temperature on a sapphire substrate whose main surface is C-plane using argon gas as a sputtering gas, and then the formed hydroxyapatite film is heated at 600 ° C. for 2 hours in oxygen gas. Heat under conditions. When formed under these conditions, the hydroxyapatite (002) peak does not appear and the crystallinity is poor. A peak attributed to CaO is also observed at a position of 2θ = 37.5 °.

  Thus, when sputter deposition is performed with argon, it is considered that the formation of large crystal domains is hindered by the Ca-excess composition. Therefore, even if argon is used as the sputtering gas, a hydroxyapatite film terminated at the C plane cannot be obtained.

  FIG. 5 also shows results of two examples in the case of solid phase growth using a sapphire substrate whose main surface is an A plane. In the case of using a sapphire substrate with the main surface being A-plane, the hydroxyapatite (211) peak is the strongest and the hydroxyapatite (002) peak is the strongest in the comparative samples annealed at 600 ° C. for 2 hours and 550 ° C. for 10 hours. It is an X-ray diffraction pattern peculiar to a hydroxyapatite polycrystalline film that is the second strongest. As is clear from this result, when a sapphire substrate having a main surface as the A plane is used, a C-plane terminated hydroxyapatite crystal film cannot be obtained at all.

Next, the conditions and crystallinity of heating (second step) after forming a film on the sapphire substrate having the C surface as the main surface will be described with reference to FIG. FIG. 6 is a characteristic diagram showing the heating temperature dependence of the Raman spectrum of a hydroxyapatite film formed by ECR sputtering on a sapphire substrate having a C-plane main surface. In FIG. 6, 380-450cm ^-1, 580cm ^-1, the peak of 750 cm ^-1 is from all the sapphire substrate.

In FIG. 6, the peak at 950 cm ⁻¹ corresponds to the symmetrical stretching mode of the PO bond of the PO ₄ ³⁻ crystal unit. Of the vibration modes of the PO ₄ ^3- unit, the only Raman-active one is this ν ₁ = 950 cm ⁻¹ . For the sample immediately after film formation (As-depo) before heating after film formation and the sample heated at 450 ° C., this peak is broad, which corresponds to the fact that it is not crystallized. On the other hand, in the sample heated at 600 ° C. for 2 hours, the peak at 950 cm ⁻¹ was very sharp, suggesting that the PO ₄ ^3- unit self-assembled into a perfect shape at the same time as crystallization. ing.

  Next, heating conditions and crystallinity after film formation on a sapphire substrate having a main surface as an A plane will be described with reference to FIG. FIG. 7 is a characteristic diagram showing the heating temperature dependence of the Raman spectrum of a hydroxyapatite film formed by ECR sputtering on a sapphire substrate whose main surface is an A-plane.

From the X-ray diffraction pattern shown in FIG. 7, it is known that all the comparative samples are randomly oriented crystals. By heating at 550 ° C. for 10 hours, at 600 ° C. for 2 hours, and at 700 ° C. for 1 hour, the peak at ν ₁ = 950 cm ⁻¹ is all sharp. The main difference from the spectrum shown in FIG. 6 is that the bending vibration mode (ν ₄ ) of PO ₄ ³⁻ is 570-610 cm ⁻¹ , and the asymmetric stretching mode (ν ₃ ) is 1050-1100 cm ^−1. It is a point that has been observed. These should be Raman-inactive by nature, but appearing on the spectrum means that the symmetry of the PO ₄ ^3- unit is broken. It is considered that the formation of polycrystals is involved in the appearance of such forbidden Raman peaks.

  Next, the contact angle of water in the hydroxyapatite film formed under each condition described above will be described with reference to FIG. FIG. 8 is a characteristic diagram showing the relationship between the heating temperature of the formed hydroxyapatite film and the contact angle of water in each of the sapphire substrate having the main surface as the C-plane and the sapphire substrate having the main surface as the A-plane. is there. The temperature is a condition for heating performed after ECR sputtering film formation.

  The contact angle of the hydroxyapatite crystal film formed on the sapphire substrate having the main surface as the C plane is in the range of 67 ° to 88 ° and is hydrophobic. On the other hand, the contact angle of the hydroxyapatite crystal film formed on the sapphire substrate whose main surface is the A plane is as low as 45 ° to 65 °. A significant difference between these is that the hydroxyapatite crystal film terminated only on the C-plane of the hydroxyapatite crystal and the hydroxyapatite crystal randomly oriented by being formed on the sapphire substrate having the main surface as the A-plane. It is clear that the difference is from the membrane.

As described above, according to the present invention, hydroxyapatite is formed on an sapphire substrate having a C-plane main surface by ECR sputtering by electron cyclotron resonance sputtering using a sputtering gas containing H ₂ O gas. Since the thin film was formed and then the thin film formed in an atmosphere containing oxygen was heated and crystallized, a hydroxyapatite thin film having a C-plane surface can be easily formed.

  By applying the present invention, it is possible to form a hydroxyapatite film made of strongly c-axis oriented crystallites even if the crystal sensitivity after film formation is in a wide range from 600 ° C. to 900 ° C. Since the obtained hydroxyapatite film gives a surface having a bone-like reactivity, the use of the hydroxyapatite film surface according to the present invention makes it possible to develop research on the interaction between the biomaterial and the bone.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious.

  101: sapphire substrate, 102: thin film.

Claims (2)

A first step of forming a thin film on a sapphire substrate having a main surface as a C-plane by an electron cyclotron resonance sputtering method using a target composed of a sintered body of hydroxyapatite and a xenon gas containing H ₂ O gas;
And a second step of crystallizing the thin film by heating in an atmosphere in which oxygen is present. A method for producing a hydroxyapatite thin film. In the manufacturing method of the hydroxyapatite thin film of Claim 1,
In the second step, heating is performed in a range of 600 ° C. to 900 ° C., and the method for producing a hydroxyapatite thin film.

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