KR101602628B1 - Manufacturing method of nanowire using atomic layer deposition - Google Patents

Abstract

The present invention relates to a method for producing nanowires on a substrate using atomic layer deposition. In particular, the platinum nanowire manufacturing method of the present invention can be easily used on a large-area substrate, and the size and shape of the nanowire can be easily adjusted, and other materials can be added.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of manufacturing a nanowire using atomic layer deposition,

The present invention relates to a method for producing a nanowire on a substrate using atomic layer deposition, and more particularly, a platinum nanowire prepared according to the method of the present invention can be used as an electrode catalyst for a fuel cell.

Atomic layer deposition (ALD) is performed by separating a precursor, which is a compound containing an element desired to be deposited, and a reactant for oxidizing or reducing the precursor, and reacting only on the surface of the substrate . The atomic layer deposition technique is specifically described in Korean Patent Publication No. 2000-0017682. Since the atomic layer deposition is a technique of depositing a thin film by surface reaction, the deposition characteristics may vary depending on the chemical condition of the surface. For example, in Lee et al., Journal of the Electrochemical Society, Vol. 157, D10, 2010, when a hydrophilic surface (SiO ₂ ) is modified to a hydrophobic surface by a chemical method, Deposition has been observed. This technique can be applied to various applications since the patterning process can be omitted. In this way, the atomic layer deposition method may or may not be deposited depending on the surface chemical reactor.

Among the various fuel cells, the proton exchange membrane fuel cell is a very active field for automotive fuel cells because it can operate at low temperatures. Hydrogen, which is fuel in the anode of the fuel cell, reacts with the catalyst and is ionized to pass through the membrane between the two electrodes to reach the cathode side and react with oxygen to produce water. At this time, electrons generated and consumed in the process of ionization and reoxidization can be used because electrons flow through an external circuit without passing through the film. Of the materials used here, the catalysts used for the anode and the cathode are very important parts, and platinum (Pt), which has the highest catalytic activity, is used. In addition, a porous carbon electrode is usually used to widen the surface area of the anode and the cathode to widen the catalytic reaction area. Since platinum is a very expensive metal, studies have been actively conducted to reduce the amount of platinum while maintaining catalytic activity to commercialize a fuel cell vehicle.

As such, the biggest obstacle to the commercialization of fuel cell vehicles is the high production cost due to expensive platinum catalysts. In order to solve this problem, attempts have been made to achieve a high catalytic activity with a small amount of platinum by preparing a nanodot type in which the surface to volume ratio of the platinum catalyst can be increased. However, when a catalyst is manufactured in the form of nano dots, the nano dots are agglomerated to decrease the reaction surface area or deteriorate easily from the electrode due to an increase in the fuel cell usage cycle. In order to solve this problem, a method of increasing the durability of the catalyst and increasing the catalytic activity efficiency has been attempted by preparing platinum in the form of a nanowire instead of the nanodot. However, there are still many problems to be solved for future mass production because the method of manufacturing the platinum nanowire is still suitable only at the laboratory level and requires a very long production time (approximately 48 hours) .

The inventors of the present invention have conducted intensive studies to solve the conventional problems as described above. As a result, they have succeeded in replacing existing platinum nanowire fabrication methods by producing nanowires on a substrate using atomic layer deposition And thus completed the present invention.

The platinum nanowire manufacturing method of the present invention can be easily used on a large-area substrate, and the size and shape of the nanowire can be easily adjusted, and other materials can be added together. In addition, since the precursor including elements such as various metals, insulators, and semiconductors in addition to platinum can be exposed to a substrate having defects in a linear form on the surface thereof, the method of the present invention can be applied to various fields Can be applied.

Fig. 1 shows an example of a method of manufacturing a nanowire according to the present invention, using a simple schematic diagram.
FIG. 2 (a) shows an SEM photograph of platinum deposited on a SiO ₂ substrate for 400 cycles using atomic layer deposition, and FIG. 2 (b) shows a SEM image of platinum deposited on a HOPG substrate for 400 cycles using atomic layer deposition (C) shows SEM images of platinum deposited on HOPG substrate for 500 cycles using atomic layer deposition, and (d) shows SEM images of platinum deposited on HOPG substrate for 600 cycles using atomic layer deposition Picture.
Figure 3 shows the diameter of platinum nanowires with increasing atomic layer deposition cycles.
Figure 4 shows a SEM photograph of ALD Pt deposited on boron nitride (BN).
FIG. 5A shows SEM photographs of the platinum nanowires (500 cycles) before the CV test, FIG. 5B shows SEM photographs of the platinum nanowires measured using the CV SEM photograph of the platinum nanowire (500 cycles) after the test is shown.

Hereinafter, the present invention will be described in detail. However, it should be understood that the present invention may be embodied in many other specific forms without departing from the spirit or essential characteristics thereof.

In one embodiment of the present invention, the present invention relates to a method for producing nanowires by exposing a precursor to a substrate surface using atomic layer deposition.

In one embodiment, the present invention can expose one precursor to a substrate surface, or sequentially expose two or more precursors to a substrate surface.

The atomic layer deposition method is a method in which deposition of a material occurs only by surface reaction, so selective deposition can be performed according to the chemical activity of the substrate used.

The substrate may be a substrate having a defect on the surface in a line shape, particularly a carbon substrate having a defect on the surface in a line shape. That is, the present invention relates to a method of manufacturing a nanowire by selectively depositing a material on a defect existing on a substrate using an atomic layer deposition method. In a preferred embodiment, the carbonaceous substrate having a line-shaped defect on the surface is highly ordered pyrolytic graphite (HOPG). The fixed-bed thermal cracking graphite substrate includes a step edge region where the surface is chemically active and a basal plane region that is chemically inert. Accordingly, the nanowire can be selectively deposited only at the step edge region where the deposited material is chemically active.

Another example of the substrate having a defect on the surface in the form of a line is boron nitride (BN), molybdenum disulfide (MoS ₂ ), and the like, but is not limited thereto.

The key idea of the present invention is that the precursor or reactant is selectively adsorbed on defective and non-defective portions of the substrate such as HOPG and is deposited by deposition of the material. Such selectivity is maintained for a certain cycle to form a material in the form of nanowires will be. Therefore, BN or MoS ₂ , which has similar defect types as HOPG The method of the present invention can be applied as it is. It is obvious that a nanowire can be manufactured by selectively depositing a material by atomic layer deposition on various substrates other than the HOPG and BN mentioned in the embodiment of the present invention.

In one embodiment, the precursor used in the method of the present invention is a compound comprising a material to be deposited, and the material to be deposited may be a metal, an insulator or a semiconductor.

The metal may be platinum (Pt), ruthenium (Ru), iridium (Ir), or a combination of one or more thereof.

The present invention is a technique maximizing the characteristics of atomic layer deposition in which deposition is performed from a surface reaction. Defects in the step edge of the substrate, such as HOPG, are chemically unstable. Therefore, it is a key mechanism of the present invention that the precursor and the reactant are more easily adsorbed to the defect, and the atomic layer deposition reaction is initiated therefrom, and the deposition selectivity is exhibited when compared with the defect free portion. Therefore, even in the atomic layer deposition process using a precursor containing a deposition material other than platinum, if the precursor or reactant is selectively adsorbed in the defective portion and the defective portion of the substrate, the present invention can be applied as it is. For example, ruthenium, iridium, and the like, which have been reported in the process of using O ₂ as the reactant, are very similar to the Pt ALD described in the embodiments of the present invention and can be used in the metal ALD process.

On the other hand, if the chemical reactivity of the precursor or the reactant is very high, the selectivity of adsorption is lost, and the growth occurs in both the defective portion and the defective portion, so that it is difficult to apply the technique proposed in the present invention. For example, halides of highly reactive and highly corrosive precursors (TiCl ₄ , AlCl ₃ Etc.), it may be difficult to apply the technique of the present invention. Also, the ALD process using a highly reactive reactant such as O ₃ may likewise be difficult to apply the present invention. In fact, O ₃ is known to form defects through etching on the graphite surface because of its high reactivity.

1 is a schematic view showing an example of a production method of the present invention using platinum. The substrate used in the present invention has a chemically active step edge and a chemically inactive base region. Platinum nuclei are formed along the step edge because selective nucleation occurs only in the chemically active part of the platinum deposited by atomic layer deposition (ALD Pt), and as the atomic layer deposition cycle increases, To form a platinum nanowire.

In another embodiment of the present invention, the present invention relates to a nanowire fabricated by the method of manufacturing a nanowire.

In one embodiment, metal nanowires such as platinum nanowires prepared in accordance with the present invention can be used as electrode catalysts for fuel cells.

By using the production method of the present invention, nanowires can be formed very easily. The atomic layer deposition method can easily control the size of the nanowires because the thickness is controlled by the growth rate (Å / cycle), which is the thickness of the deposition per cycle when the thin film is deposited. That is, according to the method of the present invention, the shape and size of nanowires can be adjusted to suit the desired application field.

In addition, it is possible to fabricate nanowires made of various materials because it is possible to easily change the material to be deposited by simply replacing the precursor. These various process advantages can be usefully employed in the preparation of various catalysts. For example, the size of nanowires can be adjusted smoothly, so you can easily find the size and shape that exhibits the best catalytic activity. In addition, alloy materials such as PtRu, which exhibit the best catalytic properties in a methanol oxidizing fuel cell, can be easily produced.

The present invention will be described in more detail with reference to the following examples. However, the following examples are for the purpose of illustrating the present invention and are not intended to limit the scope of the present invention.

[ Example ]

Pt ALD Manufacturing

The precursor used for Pt ALD was methylcyclopentadienyltrimethyl-platinum (MeCpPtMe ₃ ) and O ₂ was used as the reactant. The platinum precursor was placed in a glass canister and heated to 50 ° C to obtain a suitable vapor pressure and N ₂ was used as a carrier gas to transfer the vaporized precursor into the chamber. Platinum precursor and O ₂ The reactants were each exposed to the substrate for 2 seconds, and purging was carried out for 8 seconds while flowing only N ₂ gas therebetween. Thus, one ALD cycle consisted of four steps of platinum precursor exposure - purging - O ₂ exposure - purging, and the ALD cycle was repeated to deposit platinum. The specimen was placed on a heater and the temperature was maintained at 300 ° C. The initial specimen was loaded into the chamber and held for 30 minutes to reach 300 ° C and the ALD process was started.

(A) of FIG. 2 SiO ₂ 3 is a scanning electron microscope (SEM) image of platinum deposited on a substrate. FIG. 2 (B) is a SEM image of the HOPG substrate deposited under the same conditions. It was confirmed that the selective deposition occurred only on the HOPG substrate depending on the chemical activity of the substrate even though the deposition was performed under the same conditions. When platinum is deposited on SiO ₂ , initial nucleation is activated on a chemically active hydrophilic surface, forming a continuous thin film uniformly on the entire surface. FIG. 2 (C) and FIG. 2 (D) show the deposition of the HOPG substrate on the same conditions by increasing the deposition cycle. It was confirmed that the shape of the nanowire shape was not changed greatly but the diameter of the nanowire was increased only.

3 shows the results of measuring the diameter of the platinum nanowires along with the increase in the ALD cycle. As the cycle increases, the diameter of the nanowire increases linearly. Based on these results, it can be seen that the size of the nanowires can be easily determined by controlling the ALD cycle.

Figure 4 shows a SEM photograph of ALD Pt deposited on a boron nitride (BN) substrate. Platinum was selectively deposited along a certain line and formed into a nanowire-like shape. It was confirmed that the defect at the step edge existing at the end of one layer of BN acts as nucleation site of Pt ALD very similar to the HOPG substrate and selective deposition was performed.

CV  Test

For the CV test, one side of the HOPG substrate with a size of 1 cm x 1 cm was connected to an external electrode using a Cu tape. 0.5 M sulfuric acid solution and 0.5 M methanol solution were diluted with deionized water (DI water) and mixed at a ratio of 1: 1. The HOPG was immersed in 0.5 MH ₂ SO ₄ + 0.5 MeOH solution exactly once, and the CV was measured using a potentiostat. Ag / AgCl (KCl saturation) was used as a reference electrode and the sweep rate was measured in the range of 0 V to 1.2 V at 100 mV / s.

Figure 5 shows the results of the catalytic properties and stability of the nanowires identified through cyclic voltammetry (CV) testing. FIG. 5 (a) shows the results of 10 cycles and 500 cycles of CV measured using platinum nanowires, and it was confirmed that even after 500 cycles of CV, the catalyst characteristics showed almost no change. FIG. 5 (B) shows an SEM photograph of the platinum nanowire before the CV test, and FIG. 5 (C) shows an SEM photograph of the platinum nanowire after the CV test. As can be seen in the photograph, the shape of the nanowire was almost unchanged and no degradation such as agglomeration or detachment was observed. That is, it was confirmed that the platinum nanowires formed according to the present invention had excellent catalytic properties and were stable.

Claims (9)

By using atomic layer deposition (ALD), the precursor can be selectively exposed to the chemically active step edge and the chemically inert base surface region to expose the substrate surface to only the chemically active step edge to form a nanowire ). ≪ / RTI > The method according to claim 1,
Wherein one precursor is exposed to the substrate surface or two or more precursors are sequentially exposed to the substrate surface. delete The method according to claim 1,
Wherein the substrate is a carbon substrate. The method according to claim 1,
Characterized in that the substrate is highly ordered pyrolytic graphite (HOPG), boron nitride (BN) or molybdenum disulfide (MoS ₂ ). 3. The method according to claim 1 or 2,
Wherein the precursor is a compound containing a substance to be deposited, and the substance to be deposited is a metal, an insulator or a semiconductor. The method according to claim 6,
Wherein the metal is platinum (Pt), ruthenium (Ru), iridium (Ir), or a combination of at least one of the foregoing. delete delete

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