KR100856746B1 - Fabricating method of titania thin film - Google Patents

Abstract

A fabrication method of titania thin film is provided to mass-produce titania thin film and to obtain larger surface area of the titania thin film in a simple process by employing alumina template. A fabrication method of titania thin film comprises preparing alumina template in a process comprising steps of: debinding oil stain on the surface of aluminum substrate with acetone solution and carrying out electro-polishing of the aluminum plate in a mixture solution of perchloric acid and ethanol under a voltage(S10); carrying out the first anodizing of the aluminum plate in oxalic acid solution under a voltage(S11); removing the oxidized film on the surface of the aluminum plate to obtain the first porous oxidized film(S12); and carrying out the second anodizing of the aluminum plate and removing the oxidized film on the surface of the aluminum plate to obtain the second porous oxidized film(S13). The fabrication method of titania thin film having nanopore comprises steps of: preparing an alumina template having the second porous oxidized film; expanding the nanopore formed in the second porous oxidized film; forming PMMA mold of nanopole structure by painting liquid PMMA on the alumina template; embossing titania thin film of sol-gel state in the PMMA mold; and separating the embossed titania thin film from the PMMA mold. The fabrication method of titania thin film having nanopole or nanopipe comprises steps of: preparing an alumina template having the second porous oxidized film; forming synthesis mold of nanopore structure by painting PMMA solution on an aspect of the alumina template; embossing titania thin film of sol-gel state in the PMMA mold with the aspect having no PMMA solution of the synthesis mold; and separating the embossed titania thin film from the mold.

Description

Fabrication method of Titania thin film

1 is a view showing a method of manufacturing a titania thin film having a plurality of nanopores according to the prior art,

Figure 2 is an enlarged view showing an enlarged shape of the alumina template according to the prior art shown in Figure 1,

3 is a flowchart illustrating a method of manufacturing an alumina template for producing a titania thin film according to the present invention;

4 is a view specifically showing a preferred embodiment of the method of manufacturing the alumina template shown in FIG.

FIG. 5 is a view comparing the shapes of nanopores formed step by step in the embodiment shown in FIG. 4; FIG.

6 is a flowchart illustrating a method of manufacturing a titania thin film in which nanopores are formed in accordance with a preferred embodiment of the present invention.

7 is a view specifically showing a preferred embodiment of the method for manufacturing a titania thin film shown in FIG.

FIG. 8 is an enlarged view of the shape of nanopores or nanopoles formed step by step in the embodiment shown in FIG. 7;

FIG. 9 is a view comparing the shape of the PMMA mold according to the depth of the nanopores formed in the alumina template in the embodiment shown in FIG. 7;

10 is a flowchart illustrating a method of manufacturing a titania thin film in which nanopoles or nanopipes are formed according to an exemplary embodiment of the present invention.

11 is a view specifically showing a preferred embodiment of the method for manufacturing a titania thin film shown in FIG.

FIG. 12 is an enlarged view of the shape of nanopores, nanopoles, and nanopipes formed step by step in a preferred embodiment of the method for manufacturing a titania thin film shown in FIG. 11;

13 is a graph showing an XRD pattern of a titania thin film formed on a bare ITO substrate and an ITO substrate according to the present invention;

FIG. 14 is a graph showing EDX spectra of a bare ITO substrate and a titania thin film formed on the ITO substrate in the present invention.

 <Explanation of symbols on main parts of the drawings>

10: anodized film 11: aluminum substrate

12: Alumina Template 20: PMMA

30: titania thin film 35: ITO

The present invention relates to a method for manufacturing a titania thin film, and in particular, the structure of the nanostructures such as nano-scale pores, poles, pipes, etc. can be densely and uniformly arranged without a complicated process. It relates to a method for producing a titania thin film.

Titania is a nickname for titanium dioxide (TiO2), which is physically and chemically very stable and has a high refractive index, and is widely used in white pigments and high refractive ceramics. In particular, titania is widely used as a photocatalyst.

When using titania as a photocatalyst, it can be divided into a method of using titania as a powder and a method of forming and using a titania thin film on a specific support.In the case of forming and using a titania thin film, the production of a titania thin film can maximize the reaction area of the thin film. Research on the method is ongoing.

1 is a view showing a method for manufacturing a titania thin film having a plurality of nanopores (nanopore) according to the prior art.

In order to manufacture a titania thin film having a plurality of nanopores according to the prior art, an alumina (aluminum oxide, Al ₂ O ₃ ) template is first manufactured. The alumina template is anodized by evaporating an aluminum film of a predetermined thickness on a glass substrate, and putting it in a 0.3 M oxalic acid solution, for example, and applying a voltage.

Anodized film (Al ₂ O ₃ ) is formed on the surface of the film after the anodization treatment, and a plurality of nano-sized pores are formed on the oxide film as shown in FIG. The spacing and size of the nanopores may be controlled by the type of solution used in the anodization and the size of the voltage, and the depth of the nanopores may be controlled by the anodization time.

Next, as shown in FIG. 1B, a PMMA solution is applied to one surface of the alumina template on which the nanopores are formed to form a PMMA film that follows the shape of the alumina template, for example, using a spin coating method. The PMMA solution is applied to the template to which the PMMA solution is applied so that the applied PMMA solution is permeated with a plurality of nanopores formed in the template.

Thereafter, a PDMS solution is applied to the upper surface of the PMMA film to a predetermined thickness as shown in FIG. 1 (c). At this time, the PDMS serves as a backing layer of the PMMA film and forms the composite mold 1 together with the PMMA film.

When the PDMS is completely solidified, the alumina template is removed and separated from the synthetic mold 1. The separated synthetic mold 1 is formed with a nano-sized pole corresponding to the pore of the template on one surface in contact with the alumina template.

Next, a titania solution is applied to the ITO substrate 2 as shown in FIG. 1 (d), and the synthetic mold 1 is pressed onto the applied titania thin film. When the titania solution is solidified in the compressed state, a plurality of nanopores corresponding to each nanopole formed in the synthetic mold 1 are formed in the titania thin film, and after the titania thin film is completely solidified, the synthetic mold 1 is removed. When removed, as shown in FIG. 1 (e), a titania thin film 3 having a plurality of nanopores is obtained.

When the titania thin film is formed according to the related art as described above, the titania thin film transfers the patterns of the plurality of nanopores formed on the alumina template as it is. However, the alumina template according to the prior art described above has a problem in that the nanopores are disordered and their size is not uniformly formed as shown in FIG. 2.

FIG. 2 is an enlarged view illustrating an enlarged shape of the alumina template according to the related art shown in FIG. 1.

FIG. 2 (a) is an initial SEM image of the alumina template of the prior art, FIG. 2 (b) is an SEM image of the titania thin film after PMMA removal, and FIG. 2 (c) is an SEM image of the cross section of the titania thin film on the substrate after sintering 2 (d) is an SEM image of a titania cross-section in which pores having a size smaller than the pore diameter formed in the titania thin film of FIG. 2 (c) after sintering, and FIG. 2 (e) shows the titania thin film after PMMA removal. SEM image when viewed at large scale.

As can be seen in Figures 2 (a) to 2 (d), the alumina template according to the prior art does not have a constant size or shape of each pore formed on one surface thereof, and its depth is not formed perpendicularly to the substrate. Do not. In addition, as can be seen in Figure 2 (e) when viewed at a larger scale because the shadows appear in various parts it can be seen that the distribution of each pore is not uniform through this.

Therefore, when forming a synthetic mold of PMMA and PDMS based on the alumina template according to the prior art and forming a titania thin film, numerous nanopores formed on the titania thin film are also arranged unevenly like the nanopores of the alumina template. There is a problem that cannot utilize the thin film efficiently.

The present invention is to solve the above-mentioned problems of the prior art, and provides a method for producing a titania thin film which can produce a titania thin film of dense and uniformly arranged nanostructures using an alumina template subjected to two anodization treatment. Its purpose is to.

According to a first aspect of the present invention, there is provided a method for manufacturing a titania thin film, the method comprising: anodizing an aluminum substrate to form a first porous oxide film, wherein the first porous oxide film is formed. And forming a second porous oxide film by performing secondary anodization on the aluminum substrate from which the first porous oxide film is removed, thereby preparing an alumina template.

In addition, the method of manufacturing a titania thin film according to the second aspect of the present invention comprises the steps of preparing an alumina template on which the second porous oxide film is formed, expanding the nanopores formed on the second porous oxide film, the alumina template of Forming a PMMA mold having a nanopole structure by applying a liquid PMMA to one surface, embossing a titania thin film in a sol-gel state to the PMMA mold, and separating the embossed titania thin film. Nanopores are formed on the thin film.

In addition, in the method for manufacturing a titania thin film according to the third aspect of the present invention, preparing the alumina template on which the second porous oxide film is formed, applying a PMMA solution to one surface of the alumina template to form a synthetic mold having a nanopore structure. And embossing the titania thin film in a sol-gel state by using one surface to which the PMMA solution of the synthetic mold is not applied, and separating the embossed titania thin film from the nanopole or the titania thin film. It is characterized in that the nanopipes are formed.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

3 is a flowchart illustrating a method of manufacturing an alumina template for producing a titania thin film according to the present invention.

In step S10, in order to remove the grease that may exist on the surface of the aluminum substrate, the degreasing process is carried out with an acetone solution, and the electrolytic polishing process is performed by putting the aluminum substrate degreased in a mixed solution of perchloric acid and ethanol under a constant voltage condition. The aluminum substrate of is obtained.

In the next step S11, the aluminum substrate is placed in an oxalic acid solution of a certain concentration and subjected to voltage for oxidation treatment. Anodizing is a process of applying a strong voltage to the aluminum surface and drawing aluminum ions with the force to combine with oxygen to form aluminum oxide.

When an oxide film of Al ₂ O ₃ is formed on the aluminum substrate by the anodizing process, the oxide film formed on the aluminum substrate is removed in the next step S12.

In step S13, the aluminum substrate from which the oxide film has been removed is subjected to secondary anodization again to re-form the oxide film.

4 is a view specifically showing a preferred embodiment of the method of manufacturing the alumina template shown in FIG.

First, the pure aluminum substrate (11) without impurities is degreased in an acetone solution, and then put into a mixed solution of 60% perchlorric acid and 85% ethanol in a 1 to 5 mixture at about 3 ° C. for about 2 minutes. When electro-polishing is performed by applying a voltage of 15V, the surface of the aluminum substrate is smoothed (step S10 of FIG. 3).

Subsequently, at room temperature, the aluminum substrate 11 was placed in a 0.3 M oxalic acid solution, and the aluminum substrate 11 was connected to the positive electrode and the oxalic acid solution as the negative electrode. Then, a voltage of 50 V was applied for about 4 hours to perform a first anodizing process. As shown in FIG. 4A, a first oxide film 10 including an active layer, which is a thin layer of aluminum oxide (Al 2 O 3) initially produced during electrolysis, and a porous layer having a plurality of pores is formed (step of FIG. 3). S11).

A stripping solution (1L) is made of a chromic acid solution in which 51 ml of phosphoric acid is mixed with 18 g of chromic acid, and after the first oxide film 10 is formed, the stripping solution is formed at about 60 ° C. for 2 hours. The aluminum substrate 11 is inserted to remove the first oxide film 10 as shown in FIG. 4 (b) (step S12 of FIG. 3).

When the first oxide film 10 is removed, the aluminum substrate 11 is placed in 0.3 M of oxalic acid solution, and a second anodic oxidation treatment is performed by applying a voltage of 45 V for 40 seconds to 90 seconds to perform a second anodization. The film 12 is formed (step S13 of FIG. 3).

The present inventors believe that the pores formed in the first oxide film 10 after the first anodization are irregular in size and arrangement, but the pores formed in the second oxide film after the second anodization are As shown in Figure 4 (c) it was found that the pore of a constant size has a uniform distribution state, which will be described in detail with reference to FIG.

FIG. 5 is a view illustrating a comparison of shapes of nanopores formed step by step in FIG. 4. FIG. 5 (a) illustrates a first oxide film formed after a first anodization treatment, and FIG. b) is the second oxide film produced after the secondary anodization, Figure 5 (c) is a cross-section of the second oxide film produced after the secondary anodization for 50 seconds, Figure 5 (d) is 8 minutes SEM image showing the cross-section of the second oxide film formed after the second anodization during the process, and these were all after the pore expansion step for about 1 hour to form the PMMA mold of the nanopole structure as described below. Images.

As can be seen in FIG. 5 (a), the pores of the first oxide film formed in the first anodization process are not constant in size or arrangement, but remove the first oxide film generated during the first anodization. When the second anodization treatment is performed again, as shown in FIG. 5 (b), pores having a constant size, distribution, and arrangement state are formed.

5 (c) and 5 (d), it can be seen that in the case of the second oxide film according to the present invention, a straight pore is formed to pass through the entire alumina template. In the case of anodizing, it can be seen that each pore has a higher aspect ratio.

In brief, the reason for this phenomenon is that in the case of anodizing, a voltage is applied to an aluminum substrate, and aluminum ions in the substrate are randomly attracted to the surface and combined with oxygen to form pores. However, even if the oxide film formed in the first anodization is removed, a large number of aluminum ions are aligned on the surface of the substrate during the first anodization. Therefore, when undergoing the second anodization process as in the present invention, the nanopores are produced in the aligned state because the ions are formed in the state in which the aligned ions are arranged on the surface of the aluminum substrate during the first anodization process. It is understood.

In this case, the size of the pores generated after the secondary anodization generally depends on the anodization conditions and the conditions of the subsequent pore-widening process. The pitch and depth of the pore is proportional to the magnitude of the voltage applied during the anodization process and the anodization time, and the radius of the pore can be adjusted by changing the time of the pore expansion process at room temperature. In general, the time taken for the secondary anodization can be shorter than the time taken for the primary anodization.

On the other hand, using the alumina template formed as described above it can be produced a titania thin film having a nano-sized pore is formed. 6 is a flowchart illustrating a method of manufacturing a titania thin film in which nanopores are formed according to an exemplary embodiment of the present invention.

As described above in step S100, the aluminum substrate is prepared with an alumina template including a second porous oxide film on which nanopores are uniformly aligned by primary and secondary anodization.

In step S110, the alumina template is dipped in a predetermined solution to widen the diameter of each pore formed in the second porous oxide film.

In step S120, in order to form a PMMA mold having a nanopole structure for forming nanopores, a polymethyl meta acrylate (PMMA) solution is applied to the upper surface of the template to a predetermined thickness. The PMMA solution is subjected to heat treatment at a predetermined temperature on the alumina template to which the PMMA solution is applied so that the applied PMMA is permeated into each pore of the alumina template. After the pores are completely filled, when the PMMA solidifies, the aluminum substrate and the oxide film are removed to form a PMMA mold having one surface formed of a nanopole structure.

In step S130, a titania solution in a sol-gel state is spin-coated on an ITO substrate to form a titania thin film, and the nanopoles of the molded PMMA mold face the titania thin film before the spin coated titania thin film dries in step S140. Placed and pressed to emboss the titania thin film.

The titania thin film embossed in step S150 is dried and calcined, and the PMMA mold compressed on the titania thin film is removed in step S160 to obtain a titania thin film in which aligned nanopores are formed.

FIG. 7 is a view specifically showing a preferred embodiment of the method for manufacturing a titania thin film shown in FIG. 6.

First, as described above, after performing a degreasing and electropolishing process on the aluminum substrate 11 having no impurities mixed therein, the primary and secondary anodes are placed with 0.3 M oxalic acid solution and subjected to a constant voltage. When the oxidation treatment is performed, an alumina template is prepared in which a second porous oxide film 12 including a plurality of nanopores uniformly distributed on the aluminum substrate 11 is prepared as shown in FIG.

Subsequently, when the second porous oxide film 12 of the alumina template is dipped in 0.5 M phosphoric acid solution for 50 to 90 minutes, the respective layers formed in the porous layer of the oxide film 10 as shown in FIG. The pore diameter widens.

In order to mold the PMMA mold, PMMA having a molar mass of 350 kg / mol was dissolved in chlorobenzene to prepare a PMMA solution, and the second porous oxide film 12 having the expanded pores as shown in FIG. The upper surface of the) is applied to a predetermined thickness and heated to about 150 ℃ so that the PMMA solution 20 is completely filled in the nanopores formed on the upper surface of the second porous oxide film 12.

When the PMMA 20 coated on the upper surface of the second porous oxide film 12 is solidified, it is subjected to a wet etching process in which 4 wt% iron chloride (FeCl ₃ ) and 5M hydrochloric acid (HCl) are mixed. As shown in FIG. 7 (d), the alumina templates 11 and 12 are removed.

When the residues of the alumina templates 11 and 12 are removed by a 10% by weight sodium hydroxide (NaOH) cleaning solution, only the PMMA mold 20 in which the nanopoles are formed remains as shown in FIG. do.

Meanwhile, 1.5 g of titania (IV) ethoxide (Ti (OC ₂ H ₅ ) ₄ ), 3 g of 38% hydrochloric acid, and 10 g of 2-propanol were mixed to prepare a titania solution in a sol-gel state. The titania solution is spin coated on the ITO substrate 35 to form a titania thin film 30. Next, as shown in FIG. 7 (f), before the spin-coated titania thin film 30 is dried, the nanopoles of the PMMA mold 20 are disposed to face the titania thin film 30 to be compressed, thereby compressing the titania thin film ( Emboss 30).

The embossed titania thin film 30 was dried and sintered in a dry oven at 100 ° C. for 2 hours and the PMMA mold 20 was removed using an acetonitrile solution to form nanopore formed titania as shown in FIG. 7 (g). The thin film 30 is obtained.

8 is an enlarged view of the shape of the nanopores or nanopoles formed step by step in the embodiment shown in FIG. 7, FIG. 8 (a) is a plan view of a PMMA mold having nanopoles formed thereon, and FIG. ) Is a plan view of a titania thin film formed with nanopores according to the present invention, Figure 8 (c) is a perspective view of the titania thin film of Figure 8 (b), Figure 8 (d) is larger than the titania thin film of Figure 8 (b) An SEM image of the plan view shown in scale is shown.

As can be seen in FIG. 8 (a), the set of PMMA nanopoles is clearly revealed, in which case the high aspect ratio of the nanopoles can be achieved in a wet process. In addition, as can be seen in Figures 8 (b) to 8 (d), the PMMA mold formed with nanopoles according to the present invention follows the pattern of the alumina template with the nanopores densely and uniformly distributed, The nanopores formed in the titania thin film were also able to obtain a dense and uniformly aligned structure. In addition, the height of the nanopoles formed in the PMMA mold depends on the depth of each nanopore formed in the alumina template, which will be described below with reference to FIG. 9.

FIG. 9 is a view illustrating a comparison of the shape of the PMMA mold according to the depth of the nanopores formed in the alumina template in FIG. 7, and FIG. 9 (a) shows approximately one minute of secondary anodization. SEM image showing a cross section of the alumina template undergoing a pore expansion step of approximately 50 minutes, FIG. 9 (b) is a SEM image showing a plan view of a PMMA mold formed from the alumina template of FIG. 9 (a), and FIG. ) Is a SEM image showing a cross section of the alumina template after approximately 50 seconds of secondary anodization followed by a pore expansion step of approximately 50 minutes, and FIG. 9 (d) shows a PMMA mold formed from the alumina template of FIG. 9 (c). The plan view is a SEM image showing, and FIG. 9 (e) is a SEM image showing a cross section of the alumina template which has undergone a pore expansion step of approximately 50 minutes after a second anodization treatment of approximately 40 seconds, and FIG. e) alumina template From a SEM image showing a plan view of a mold that is molded PMMM.

As shown in FIG. 9 (a), the secondary porous oxide film has a depth of about 320.72 nm in the case of the alumina template subjected to approximately one-second secondary anodization. When the PMMA mold is molded from the alumina template, the ends of most nanopoles are entangled with each other, as shown in FIG. 9 (b), so that nanopores cannot be properly formed on the titania thin film.

In addition, in the case of the alumina template subjected to 50 seconds of secondary anodization as shown in FIG. 9 (c), the secondary porous oxide film has a depth of about 270 nm, but in this case, as shown in FIG. As shown in FIG. 9 (b), the number of nanopoles in the PMMA mold was still entangled with each other.

However, as shown in FIG. 9 (e), the alumina template subjected to secondary anodization of about 40 seconds has a secondary porous oxide film having a depth of about 230 nm, and the PMMA mold formed therefrom is shown in FIG. As shown in f), with the exception of a few nanopoles, most of the nanopoles are erected straight without intertwining with each other. Therefore, in forming a titania thin film having nanopores, it is preferable that the PMMA mold be molded from an alumina template subjected to secondary anodization of approximately 40 seconds.

In the present invention, PMMA polymers are used to replicate nanoporous alumina templates intact, for example, to have a significantly higher strength than other organic materials so that dense and well-defined nanostructures can be replicated and formed without distortion. . In addition, since the PMMA polymer is chemically stable within a wide pH range, even when wet etching aluminum and alumina, its structure can be maintained without being deformed. In particular, the PMMA polymer does not dissolve in alcohol-based solutions such as 2-propanol, which is required to make a sol-gel titania solution, but selectively dissolves in some organic solvents, so that the PMMA mold is later removed without damaging the nanoporous titania thin film. There is an advantage that can be removed.

Meanwhile, the titania thin film is spin coated in a sol-gel state, and the spin coated titania thin film may be uniformly patterned by nanoimprinting lithography technology using an alumina template. Therefore, if the PMMA mold is removed with acetonitrile for 4 hours, a uniform nanoporous titania thin film as shown in FIG. 8 (b) can be obtained, and the pattern formed on the template is preserved as it is in the structure of the titania thin film. Able to know. In this case, as shown in FIGS. 8B and 8C, the diameters and the pore distances of the pores formed in the titania thin films were formed at 80 nm and 50 nm, and the depths thereof were extended to 130 nm. Referring to Figure 8 (d) it can be seen that the nanopores formed on the titania thin film according to the present invention are very uniformly aligned.

According to another preferred embodiment of the present invention, uniform nanopoles or nanopipes may be formed on the titania thin film using the alumina template subjected to the first and second anodization processes as described above.

10 is a flowchart illustrating a method of manufacturing a titania thin film in which nanopoles or nanopipes are formed according to an exemplary embodiment of the present invention.

First, an alumina template having a second porous oxide film formed by the first and second anodizing methods as described above in step S200 is prepared. In step S210, the PMMA solution is applied on the second porous oxide film of the alumina template to a predetermined thickness, for example, using a spin coating method. The PMMA film coated on the second porous oxide film performs a function of a backing layer for supporting the second porous oxide film, and forms a composite mold together with the second porous oxide film. . Therefore, when forming the PMMA film, a part of the applied PMMA should not be penetrated into the nanopores of the second porous oxide film. Then, after removing the aluminum substrate which is the active layer of the alumina template in step S220, the shape of the plurality of holes that the nanopores remaining on the second porous oxide film almost passes through the upper and lower surfaces of the second porous oxide film (the second The porous oxide film is left with a thin barrier layer by anodization.

In the next step S230 to widen the diameter of the nanopores formed in the second porous oxide film of the synthetic mold.

In step S240, spin coating a titania solution in a sol-gel state on an ITO substrate, and in step S250, one surface of the synthetic mold on which the ITO substrate and the nanopores are formed are disposed to face each other, and the spin coated titania solution is disposed therebetween. Before solidifying, the titania thin film is embossed according to the nanoporous structured synthetic mold by pressing the composite mold onto the ITO substrate. In this case, the titania solution spin-coated on the ITO substrate by the pressure on the synthetic mold flows into the nanopores formed in the secondary porous oxide film.

In step S260, the embossed template and the substrate are dried and sintered, and in step S270, the combined PMMA film and the second porous oxide film are sequentially removed to obtain a titania thin film in which nanopoles or nanopipes are formed.

FIG. 11 is a view illustrating a preferred embodiment of the method for manufacturing a titania thin film shown in FIG. 10 in detail.

First, as described above, degreasing and electropolishing processes are performed on the aluminum substrate 11 having no impurities mixed therein, and then the first and second anodization treatments are performed by placing the aluminum substrate 11 in a 0.3 M oxalic acid solution and applying a constant voltage. As shown in FIG. 11A, an alumina template having a second porous oxide film 12 including a plurality of nanopores uniformly distributed on the aluminum substrate 11 is prepared. In this case, the diameters and pitches of the nanopores formed on the second porous oxide film 12 were 40 nm and 110 nm, respectively.

Next, as shown in FIG. 11 (b), the PMMA solution 20 is prepared, spin-coated on the second porous oxide film 12, and solidified by heating at about 100 ° C., followed by saturated iron chloride (FeCl). ₃ ) A synthetic mold consisting of the second porous oxide film 12 and the PMMA film 20 is formed by immersing in a solution and dissolving and removing the aluminum layer 11 as shown in FIG. Thereafter, the synthetic mold was dipped in a 0.5 M phosphoric acid solution for about 90 minutes to remove residue on the synthetic mold (including the barrier layer remaining on the second porous oxide film) and at the same time the second porous oxide. The diameter of each nanopore formed in the film 12 is widened.

Meanwhile, 1.8 g of titania (IV) ethoxide (Ti (OC 2 H 5) 4), 0.3 g of 38% hydrochloric acid, and 8 g of 2-propanol were mixed to prepare a titania solution in a sol-gel state. The titania solution is spin coated on the ITO substrate 35 to form a titania thin film 30. Next, as shown in FIG. 11D, before the spin-coated titania thin film 30 is dried, the nanopores formed on the second porous oxide film 12 face the titania thin film 30. The composite mold is placed and pressed to emboss the titania thin film 30.

The embossed titania thin film 30 was dried and sintered in a dry oven at 100 ° C. for 3 hours and the PMMA film 20 and the second porous oxide film 12 were removed using acetonitrile and the stripping solution. As shown in f), a titania thin film 30 in which nanopoles are formed is obtained.

In this case, in order to form a nanopipe shape having a hollow instead of a nanopole shape in order to further reduce the surface area of the titania thin film, 1 g of the titania (IV) ethoxide (Ti (OC2H5) 4) is used. Same as in the case of nanopole.

FIG. 12 is an enlarged view of the shape of nanopores or nanopoles formed step by step in a preferred embodiment of the method for manufacturing a titania thin film shown in FIG. 11. 12 (a) is a plan view of the alumina template is formed nano-pores, Figure 12 (b) is a plan view when the nano-pores on the synthetic mold formed by using the alumina template of Figure 12 (a), Figure 12 (c And (d) are SEM images showing a plan view and a cross-sectional view of a titania thin film formed with nanopoles according to the present invention, and FIGS. 12 (e) and 12 (f) are titania formed with nanopipes according to the present invention. It is an SEM image which shows the top view and sectional drawing of a thin film.

12 (a) and 12 (b), the diameters and pitches of the pores on the second porous oxide film before the nanopores were expanded in this embodiment were 40 and 110 nm, respectively, and in FIG. 12 (b). As shown, when the pore expansion treatment is performed for approximately 90 minutes, it can be seen that similarly to FIG. 5 (b), pores are well aligned at uniform intervals without defects. In addition, as can be seen in Figure 12 (c), according to this embodiment, all of the nanopoles having a diameter and height of approximately 70 to 180nm on the titania thin film were formed in a straight line in parallel with each other. In Figure 12 (c) some defects are observed throughout, but this is presumed to be due to the defects of nanopores on the alumina template and the amount of irregular spin coating of the sol-gel solution. In addition, referring to Figure 12 (d) it can be seen that the nanopoles formed on the titania thin film is formed in a straight line substantially parallel to each other according to the present invention. In addition, it can be seen that the nanopole according to the present invention has a high aspect ratio and has a structure capable of emitting a large amount of electrons more efficiently.

In addition, the nanopipes that can be formed in the titania thin film according to the present invention can be produced by controlling the amount of titania. In other words, if the titania solution does not contain enough titania particles to form nanopoles, the sintering will cause the titania particles to stick around the walls of the alumina template. The thin film forms the shape of a nanopipe having a hollow in the center thereof. 12 (e) and 12 (f) are plan and cross-sectional views of the titania thin film when 1 g of titania (IV) ethoxide (Ti (OC2H5) 4) is used instead of 1.8 g, and referring to the outer diameter of the nanopipe It can be seen that the inner diameter and the height can be formed in sizes of 110 nm, 30 nm and 200 nm.

FIG. 13 is a graph showing an XRD pattern of a bare ITO substrate and a titania thin film formed on an ITO substrate according to the present invention, and FIG. 13 (a) shows an XRD pattern of a bare ITO substrate, and FIGS. 13 (b) to FIG. 13 (d) shows the XRD patterns when the ITO substrate on which the titania thin film is formed is heat-treated at 150 ° C., 400 ° C. and 500 ° C. for about 30 minutes, respectively.

It can be seen from FIG. 13 that the peak of the 101 anatase crystal plane of titania, distinct from the bare ITO peak (FIG. 13 (a)), is clearly observed. Generally thin film titania peaks can be observed when sintered at about 400 ° C., but no peaks were observed in this example (see FIG. 13 (c)). However, it can be seen that when heated to 500 ° C., the diffraction peak showing the anatase crystal phase appears in the XRD pattern of the ITO substrate (see FIG. 13 (d)).

It is understood that the sintering temperature of at least 500 ° C. causes the titania thin film according to the present invention to have an anatase crystal phase. The titania thin film can make the most of the function of the electron emission source in the state of the anatase crystal phase.

FIG. 14 is a graph showing EDX spectra of a bare ITO substrate and a titania thin film formed on the ITO substrate in the present invention. 14 (a) and 14 (b) are diagrams showing EDX spectra of titania thin films on the bare ITO substrate and the ITO substrate and corresponding integral concentrations of the components in the thin films, respectively.

The EDX spectrum of the bare ITO substrate has a high diffraction peak of indium, tin, and silicon oxide, as shown in FIG. 14 (a). Thus, it can be seen that the ITO substrate includes the above elements. However, when the titania thin film coated on the ITO substrate was heated at 500 ° C. for 30 minutes, as shown in FIG. 14B, the diffraction peaks of titanium and oxygen, which are members of titania, were observed in the EDX spectrum of the ITO substrate coated with the titania thin film. In addition, it can be seen that the diffraction peak for nitrogen also appears.

This is because nitrogen contained in the surrounding air combines with titanium when the titania thin film is heated at 500 ° C., and thus the titania thin film is actually formed from TiO ₂ , TiO, TiN. In particular, when TiN is irradiated with light in the visible light region between 370 nm and 550 nm, the photoreaction of nitrogen-doped titania is increased to improve the conversion efficiency of the photovoltaic cell.

As described above, the method for manufacturing a titania thin film having a nanostructure according to the present invention has been described with reference to the illustrated drawings. However, the present invention is not limited to the embodiments and drawings disclosed herein, and uses an alumina template and a synthetic mold. It is apparent that the technical idea of the present invention for preparing a titania thin film of densely aligned nanostructures can be easily applied by those skilled in the art within the scope of the claims.

The method of manufacturing a titania thin film having a nanostructure according to the present invention configured as described above is a nanopore, nanopole, nanopipe, etc., which are densely and uniformly arranged using an alumina template, a PMMA mold, or a synthetic mold without a complicated process. Titania thin film having a structure can be manufactured, and mass production can be performed at a low cost, and a titania thin film having a largely increased surface area can be manufactured compared to the conventional one, thus greatly improving the operation efficiency when used as a photovoltaic cell and a photocatalyst. It can be effected.

Claims (18)

First anodizing the aluminum substrate to form a first porous oxide film; Removing the first porous oxide film; And Forming a second porous oxide film by performing secondary anodization on the aluminum substrate from which the first porous oxide film has been removed. Method for producing a titania thin film comprising the step of preparing an alumina template comprising a. The method of claim 1, The removing of the first porous oxide film may include removing the first porous oxide film by placing the aluminum substrate on which the first porous oxide film is formed in a chromic acid solution containing 18 g of phosphoric acid at 60 ° C. Titania thin film manufacturing method. The method of claim 1, Before the first anodization, the method of manufacturing a titania thin film comprising the step of degreasing and electropolishing the aluminum substrate. The method of claim 1, The first anodization treatment is a method of manufacturing a titania thin film, characterized in that by placing the aluminum substrate in 0.3M oxalic acid solution and applying a voltage of 50V for 4 hours. The method of claim 1, The secondary anodization treatment is a method of manufacturing a titania thin film, characterized in that the aluminum substrate from which the first porous oxide film has been removed is placed in a 0.3 M oxalic acid solution and a voltage of 45 V is applied for 40 to 90 seconds. Preparing an alumina template on which the second porous oxide film according to claim 1 is formed; Expanding the nanopores formed in the second porous oxide film; Forming PMMA mold having a nanopole structure by applying liquid PMMA to the alumina template; Embossing a titania thin film in a sol-gel state on the PMMA mold; And Separating the embossed titania thin film from the PMMA mold Method for producing a titania thin film, characterized in that the nanopore is formed, including. The method of claim 6, The titania thin film in the sol-gel state comprises 1.8 g of titania (IV) ethoxide and 8 g of 2-propanol. The method of claim 6, The nanopore expansion step is a method of manufacturing a titania thin film, characterized in that for dipping (alupping) the alumina template in 0.5M phosphate solution for a predetermined time. The method of claim 7, wherein Forming the PMMA mold of the nanopole structure, Heat treating the alumina template to which the PMMA solution is applied at a predetermined temperature so that the applied PMMA is infiltrated into the expanded nanopores of the alumina template. The method of claim 6, The embossing step, Spin coating the titania solution in sol-gel state on an ITO substrate; And Before the spin-coated titania solution solidifies, placing and compressing a plurality of nanopoles formed in the PMMA mold to face the titania solution Method for producing a titania thin film, characterized in that comprises a. The method of claim 6, The separating step, Drying and sintering the embossed PMMA mold and the titania thin film; And Removing the PMMA mold Method for producing a titania thin film, characterized in that comprises a. Preparing an alumina template on which the second porous oxide film according to claim 1 is formed; Forming a synthetic mold having a nanopore structure by applying PMMA solution to one surface of the alumina template; Embossing the titania thin film in a sol-gel state by using one side of the synthetic mold to which the PMMA solution is not applied; And Separating the embossed titania thin film Method for producing a titania thin film, characterized in that comprises a nano-pole or nano-pipe formed. The method of claim 12, Forming the synthetic mold of the nanopore structure, Thermally treating the alumina template coated with the PMMA solution to a predetermined temperature; Removing the active layer of the aluminum template except for the second porous oxide film; And Titania thin film manufacturing method comprising the step of expanding the nanopores formed in the second porous oxide film. The method of claim 13, The nanopore expansion step is a method for producing a titania thin film, characterized in that for dipping the alumina template in 0.5M phosphate solution for a predetermined time. The method of claim 12, The titania solution in the sol-gel state is a method for producing a titania thin film, characterized in that the nanopoles are formed including 1.8 g of titania (IV) ethoxide and 8 g of 2-propanol. The method of claim 12, The titania solution of the sol-gel state is a method for producing a titania thin film, characterized in that the nanopipes are formed containing 1 g of titania (IV) ethoxide and 8 g of 2-propanol. The method of claim 12, The embossing step, Spin coating the titania solution in sol-gel state on an ITO substrate; And Before the spin-coated titania solution solidifies, placing a plurality of nanopores formed on the second porous oxide film toward the titania solution to compress the composite mold Method for producing a titania thin film, characterized in that comprises a. The method of claim 12, The separating step, Drying and sintering the embossed composite mold and the titania thin film; And Removing the PMMA film and the second porous oxide film Method for producing a titania thin film, characterized in that comprises a.

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