Method for forming metal nanowire or metal nanomesh

Abstract

The present invention relates to a method for forming a metal nanowire or a metal nanomesh. More particularly, the present invention relates to a method for forming a metal nanowire or a metal nanomesh capable of forming a variety of metal nanowires or metal nanomeshes in a desired shape by a simplified method. The method for forming a metal nanowire or a metal nanomesh includes the steps of forming a block copolymer thin film on a substrate, in which the block copolymer thin film includes specific hard segments and soft segments containing one or more polymer repeating units selected from the group consisting of a poly(meth)acrylate-based repeating unit, a polyalkylene oxide-based repeating unit, a polyvinylpyridine-based repeating unit, a polystyrene-based repeating unit, a polydiene-based repeating unit and a polylactone-based repeating unit; conducting orientation of the hard segments and soft segments in a lamellar or cylindrical form in the block copolymer thin film; selectively removing the soft segments; adsorbing a metal precursor onto the hard segments; and removing the hard segments.

Claims

1. A method for forming a metal nanowire or a metal nanomesh, comprising the steps of: forming a block copolymer thin film on a substrate, in which the block copolymer thin film includes hard segments containing a repeating unit of Chemical Formula 1 and soft segments containing a poly(meth)acrylate-based repeating unit of Chemical Formula 2; conducting orientation of the hard segments and soft segments in a lamellar or cylindrical form in the block copolymer thin film; adsorbing an oxide of a transition metal onto the block copolymer thin film, in which the oxide of a transition metal is selectively adsorbed onto the hard segments; selectively removing the soft segments; adsorbing a metal precursor onto the hard segments; and removing the hard segments and forming the metal nanowire or the metal nanomesh, by treating the hard segments with oxygen plasma: ##STR00007## in Chemical Formula 1, n is an integer of 5 to 600, R is hydrogen or methyl, R is X, ##STR00008## X is ZR, Y is alkylene having 1 to 10 carbon atoms, Z is arylene having 6 to 20 carbon atoms, R is a linear or branched hydrocarbon having 10 to 20 carbon atoms, or a linear or branched perfluorohydrocarbon having 10 to 20 carbon atoms, in Chemical Formula 2, m is an integer of 30 to 1000, R.sub.1 and R.sub.2 are methyl, wherein the step of adsorbing an oxide of a transition metal onto the block copolymer thin film, the block copolymer thin film is treated with a solution including 0.05 to 1.0 wt % of RuO.sub.4 or OSO.sub.4, wherein the hard segment is a crystalline hard segment, wherein the crystalline hard segment and the block copolymer including the same has a melting point (Tm) of 200 to 300 C., and the soft segment has a glass transition temperature (Tg) of 40 to 130 C., and wherein the step of conducting orientation includes a step of conducting solvent annealing of the block copolymer thin film or conducting heat treatment at a temperature higher than the melting point of the hard segment and the glass transition temperature of the soft segment.

2. The method of claim 1, wherein the block copolymer includes 10 to 90 wt % of the hard segment and 90 to 10 wt % of the soft segment.

3. The method of claim 1, wherein a plurality of nanowires having a line width of 5 to 50 nm are formed at a spacing of 5 to 100 nm.

4. The method of claim 1, wherein a plurality of nanomeshes having a diameter of 5 to 70 nm are formed at a spacing of 5 to 100 nm.

5. The method of claim 1, wherein by the orientation step, the hard segments and soft segments are arranged in a lamellar or cylindrical form which is vertical to the substrate, and the cylindrical form is arranged in a square or hexagonal honeycomb shape in a top-down view of the substrate.

6. The method of claim 1, wherein the step of selectively removing the soft segments includes a step of UV irradiation of the block copolymer thin film.

7. The method of claim 1, wherein the metal precursor is used in the form of a neutral metal salt aqueous solution.

8. The method of claim 7, wherein the neutral metal salt includes Na.sub.2PtCl.sub.4, Na.sub.2PdCl.sub.4, K.sub.3Fe(CN).sub.6, K.sub.3Co(CN).sub.6, KAg(CN).sub.2, CuCl.sub.2.6H.sub.2O or HAuCl.sub.4.

9. The method of claim 1, wherein the metal precursor is prepared from a cation of a metal selected from the group consisting of Pt, Pd, Co, Fe, Ni, Au, Ti, Cu, Ta, W and Ag.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1a is an SEM photograph of the surface of a lamellar-shaped nanostructure, after removal of soft segments which were decomposed by UV irradiation of the lamellar-shaped nanostructure formed on the surface of a polymer thin film in Example 5;

(2) FIG. 1b is an SEM photograph of the surface and cross section of a Pt metal nanowire finally formed in Example 5;

(3) FIG. 2 is an SEM photograph of the surface and cross section of a Fe metal nanowire finally formed in Example 6;

(4) FIG. 3 is an SEM photograph of the surface and cross section of a Co metal nanowire finally formed in Example 6;

(5) FIG. 4 is an SEM photograph of the surface and cross section of an Ag metal nanowire finally formed in Example 6;

(6) FIG. 5 is an SEM photograph of the surface and cross section of an Au metal nanowire finally formed in Example 6;

(7) FIG. 6a is an SEM photograph of the surface of a cylindrical nanostructure, after removal of soft segments which were decomposed by UV irradiation of the cylindrical nanostructure arranged in a hexagonal shape on the surface of a polymer thin film in Example 7;

(8) FIG. 6b is an SEM photograph of the surface and cross section of a Pt metal nanowire finally formed in Example 7;

(9) FIG. 6c is an SEM photograph of the surface of a Fe metal nanomesh finally formed in Example 8;

(10) FIG. 6d is an SEM photograph of the surface of a Co metal nanomesh finally formed in Example 8;

(11) FIG. 6e is an SEM photograph of the surface of an Ag metal nanomesh finally formed in Example 8; and

(12) FIG. 7 is XPS analysis data of the binding energy of various metal nanowires prepared in Examples 5 and 6.

EXAMPLES

(13) Hereinafter, the function and effect of the present invention will be described in more detail with reference to the specific Examples of the present invention. However, these Examples are only to illustrate the invention and are not intended to limit the scope of the invention.

Examples 1 to 4: Preparation of Macroinitiator and Block Copolymer

[Example 1]: Preparation of Macroinitiator (Macro-PMMA)-1

(14) 6.0 g of monomers MMA, 66.3 mg of a RAFT reagent cyanoisopropyldithiobenzoate, 24.6 mg of a radical initiator AIBN, and 6.82 mL of benzene were poured into a 20 mL-glass ampoule, and oxygen was removed from the solution by freeze-thawing, and then the ampoule was sealed, and RAFT polymerization was conducted in an oil container of 60 C. for 24 hours. After polymerization, the reaction solution was precipitated in 200 mL of an extraction solvent methanol, filtered under reduced pressure, and dried to prepare a pink macroinitiator (Macro-PMMA)-1 in which the RAFT reagent is bound to both ends of MMA (PMMA) polymer. The polymerization conversion, number average molecular weight (M.sub.n), molecular weight distribution (M.sub.w/M.sub.n) and glass transition temperature (T.sub.g) were 95%, 19700, 1.14 and 119 C., respectively.

[Example 2]: Preparation of Novel Block Copolymer-1

(15) 0.732 g of the acrylamide-based monomer DOPAM synthesized in Example 1 of Korean Patent NO. 1163659, 0.45 g of the macroinitator-1 prepared in Example 1, 2.54 mg of AIBN, and 3.794 mL of benzene were poured into a 10 mL Schlenk flask, stirred at room temperature for 30 minutes under nitrogen atmosphere, and then RAFT polymerization was conducted at a silicon oil container of 70 C. for 72 hours. The polymer solution was precipitated in 200 mL of methanol, and then filtered under reduced pressure, and dried to prepare a light yellow block copolymer-1 (PMMA-b-PDOPAM-1). The composition ratio of the hard segment vs. the soft segment in the block copolymer-1 (ratio of number average molecular weight measured by GPC) was 47 wt % vs. 53 wt %. The polymerization conversion, number average molecular weight, molecular weight distribution, T.sub.g and melting temperature (T.sub.m) were 55%, 37000, 1.25, 119 C., 235 C., respectively.

[Example 3]: Preparation of Macroinitiator (Macro-PMMA)-2

(16) A pink macroinitiator (Macro-PMMA)-2 was prepared in the same manner as in Example 1, except that 4.085 g of the monomer MMA, 90.3 mg of a RAFT reagent cyanoisopropyldithiobenzoate, 33.5 mg of a radical initiator AIBN, and 4.684 mL of benzene were used. The polymerization conversion, number average molecular weight (M.sub.n), molecular weight distribution (M.sub.w/M.sub.n) and glass transition temperature (T.sub.g) were 90%, 10800, 1.15 and 119 C., respectively.

[Example 4]: Preparation of Novel Block Copolymer-2

(17) A novel light yellow block copolymer-2 (PMMA-b-PDOPAM-2) was prepared in the same manner as in Example 2, except that 0.774 g of the acrylamide-based monomer DOPAM synthesized in Example 1 of Korean Patent NO. 1163659, 0.3 g of the macroinitator-2 prepared in Example 3, 3.0 mg of AIBN, and 4.011 mL of benzene were used. The composition ratio of the hard segment vs. the soft segment in the block copolymer-2 (ratio of number average molecular weight measured by GPC) was 66 wt % vs. 34 wt %. The polymerization conversion, number average molecular weight, molecular weight distribution, T.sub.g and T.sub.m were 66%, 29400, 1.30, 119 C., 235 C., respectively.

Example 5 to 6: Formation and Identification of Various Metal Nanowires

[Example 5]: Formation of Pt Metal Nanowire Using Block Copolymer-1

(18) The block copolymer-1 (PMMA-b-PDOPAM-1) prepared in Example 2 was dissolved in a chloroform solvent to prepare a 0.5 wt % solution thereof, which was then coated on a substrate of a silicon wafer, in which SiO.sub.2 was applied on the surface thereof, at 3000 rpm for 60 seconds using a spin coater to form a thin film. The block copolymer thin film thus prepared was put in a desiccator that was maintained under atmosphere of the stream of a mixed solvent of THF/cyclohexane 8/2 (v/v, volume ratio), and aged for 24 hours to manifest a lamellar nanostructure on the surface of the thin film.

(19) The thin film having the lamellar nanostructure was put in a vial containing 0.4 wt % RuO.sub.4 liquid for 4 minutes to adsorb RuO.sub.4 on the thin film, and then irradiated with UV at 254 nm for 15 minutes to decompose the soft segments (PMMA). Subsequently, the film was put in 3 mL of 20 mM Na.sub.2PtCl.sub.4 aqueous solution for 3 hours, and then taken out and washed with water several times to remove the decomposed soft segments, and then dried to prepare a thin film in which Pt metals were adsorbed onto the hard segments (PDOPAM). This film was treated with oxygen plasma (40 sccm; 50 W; 60 sec) to form a lamellar Pt metal nanowire.

(20) FIG. 1a is an SEM photograph of the surface of a lamellar nanostructure, after removal of soft segments which were decomposed by UV irradiation of the lamellar nanostructure formed on the surface of a polymer thin film. FIG. 1b is an SEM photograph of the surface and cross section of a Pt metal nanowire which was formed by removing hard segments by oxygen plasma treatment, after selective adsorption of Pt metal ions onto the hard segments in the lamellar nanostructure of FIG. 1a. Referring to FIGS. 1a and 1b, it was confirmed that the Pt metal nanowires are well-arranged on a silicon substrate having a wide area (43 m). The line width and spacing of the Pt metal nanowires were about 20 nm and about 39 nm, respectively.

[Example 6]: Formation of Various Metal Nanowires Using Block Copolymer-1

(21) Various lamellar metal nanowires of Fe, Co, Ag, or Au were formed in the same manner as in Example 5, except that a K.sub.3Fe(CN).sub.6, K.sub.3Co(CN).sub.6, KAg(CN).sub.2, or HAuCl.sub.4 aqueous solution was used as a metal precursor, instead of Na.sub.2PtCl.sub.4 aqueous solution. The surface and cross section of the Fe, Co, Ag, or Au metal nanowire were analyzed by SEM, and photographs thereof are shown in FIGS. 2 to 5. Referring to FIGS. 2 to 5, it was confirmed that the metal nanowires were well-arranged on a silicon substrate having a wide area (43 m).

(22) At this time, the metal nanowires composed of the metals were identified by measuring their own binding energy of the various metals by XPS (X-ray Photoelectron Spectroscopy). FIG. 7 is analysis data of the binding energy of various metal nanowires prepared in Examples 5 and 6. As a result, it was confirmed that the metal nanowires were well-prepared.

Example 7 to 8: Formation and Identification of Various Metal Nanomeshes

[Example 7]: Formation of Pt Metal Nanomesh Using Block Copolymer-2

(23) The block copolymer-2 (PMMA-b-PDOPAM-2) prepared in Example 4 was dissolved in a chloroform solvent to prepare a 0.5 wt % solution thereof, which was then coated on a substrate of a silicon wafer, in which SiO.sub.2 was applied on the surface thereof, at 3000 rpm for 60 seconds using a spin coater to form a thin film. The block copolymer thin film thus prepared was put in a desiccator that was maintained under atmosphere of the stream of a mixed solvent of THF/cyclohexane 8/2 (v/v, volume ratio), and aged for 24 hours to manifest a cylindrical nanostructure arranged in a hexagonal shape on the surface of the thin film.

(24) The thin film having the cylindrical nanostructure was put in a vial containing 0.4 wt % RuO.sub.4 liquid for 4 minutes to adsorb RuO.sub.4 on the thin film, and then irradiated with UV at 254 nm for 15 minutes to decompose the soft segments (PMMA). Subsequently, the film was put in 3 mL of 20 mM Na.sub.2PtCl.sub.4 aqueous solution for 3 hours, and then taken out and washed with water several times to remove the decomposed soft segments, and then dried to prepare a thin film in which Pt metals were adsorbed onto the hard segments (PDOPAM). This film was treated with oxygen plasma (40 sccm; 50 W; 60 sec) to form a honeycomb-shaped Pt metal nanomesh.

(25) FIG. 6a is an SEM photograph of the surface of a cylindrical nanostructure, after removal of soft segments which were decomposed by UV irradiation of the cylindrical nanostructure formed on the surface of a polymer thin film. Referring to FIG. 6a, it was confirmed that black nanomesh patterns from which soft segments were selectively removed were well-arranged in a two-dimensional hexagonal honeycomb shape. It was also confirmed that the diameter of each nanopattern of the cylindrical shape and the spacing (pitch) were about 15 nm and about 30 nm, respectively. FIG. 6b is an SEM photograph of the surface of a Pt metal nanomesh which was formed by removing hard segments by oxygen plasma treatment after selective adsorption of Pt metal ions onto the hard segments in the cylindrical nanostructure of FIG. 6a. It was confirmed that the diameter and spacing of the Pt metal nanomesh were about 19 nm and about 31 nm, respectively. Further, the above described XPS analysis technique was performed to confirm that large honeycomb-shaped Pt metal nanomeshes were well-formed. The results are the same as in FIG. 7.

[Example 8]: Formation of Various Metal Nanomeshes Using Block Copolymer-2

(26) Various metal nanomeshes of Fe, Co or Ag were formed in the same manner as in Example 7, except that a 30 mM K.sub.3Fe(CN).sub.6, K.sub.3Co(CN).sub.6, or KAg(CN).sub.2 aqueous solution was used as a metal precursor, instead of Na.sub.2PtCl.sub.4 aqueous solution. The surface of the Fe (diameter=about 15 nm; spacing=about 31 nm), Co (diameter=about 15 nm; spacing=about 31 nm) or Ag (diameter=about 19 nm; spacing=about 31 nm) metal nanomesh was analyzed by SEM, and photographs thereof are shown in FIGS. 6c to 6e. Referring to FIGS. 6c to 6e, it was confirmed that the honeycomb-shaped metal nanomeshes were well-arranged on a silicon substrate having a wide area (43 m).

(27) Further, the above described XPS analysis technique was performed to confirm that a variety of large honeycomb-shaped metal nanomeshes were well-formed. The results are the same as in FIG. 7.