KR101705699B1 - Indium oxide nanorods coated with bismuth oxide and Method of preparing for the same - Google Patents

Abstract

The present invention relates to an indium oxide nano-rod coated with bismuth oxide and a method of preparing the same. More specifically, provided is an indium oxide nano-rod coated with bismuth oxide for detection of gas, which comprises: an indium oxide nano-rod; and a bismuth oxide nanoparticle coating layer applied to a surface of the nano-rod The indium oxide nano-rod coated with bismuth oxide according to the present invention is prepared using indium sulfide powder, not conventionally used indium or indium oxide power, so a nano-rod with a fine diameter can be prepared. In addition, since bismuth powder is mixed at a proper ratio, a p/n junction composite nano rod can be synthesized without relative material dispersion between the indium oxide and bismuth oxide. Moreover, compared with single-structured nano materials, gas detection performance may be improved due to enhancement of catalytic characteristics of materials, gas adsorption on interfaces, increase of potential barriers, and increase of depletion layers, and especially, it is possible to prepare a nano-rod sensor specialized in the detection of ethanol gas.

Description

TECHNICAL FIELD The present invention relates to indium oxide nanorods coated with bismuth oxide and to a method for preparing the same.

The present invention relates to a bismuth oxide coated indium oxide nanorod and a method for producing the same, and more particularly, to a method for producing an indium oxide nanorod having a bismuth oxide nanoparticle formed on a surface thereof and a method for producing a bismuth oxide coated oxide indium It is about nanorods.

The metal oxide semiconductor (MOS) material has a higher detection characteristic and faster detection or recovery reaction rate, low concentration gas detection capability, lower production cost, easy synthesis method, and high durability Which is very advantageous for use as a gas detecting element material. On the other hand, a disadvantage that a high operating temperature is required in the detection reaction is also present. Therefore, in order to fabricate such a MOS-based gas detection sensor, it is necessary to increase the detection characteristic and to lower the operating temperature.

One solution to this problem is to fabricate nanodevices. Since the volume-to-surface area ratio of a zero-dimensional or one-dimensional nano device is very high, the amount of detection gas adsorbed or desorbed on the surface of the device during gas detection reaction becomes very high, Very high. In addition, the characteristics of nanomaterial devices for gas detection can be improved by doping MOS materials with different materials, by coating nanoparticles with different characteristics on the surface, and by coating these materials.

The elements used for such doping include various lanthanides and actinides, various transition elements, and MOS doped materials with different element sizes and doping properties. Through this, an artificial lattice defect or lattice mismatch is caused to improve the gas adsorption through the gap. In addition, when nanoparticles are coated on the surface, it is possible to improve the reaction characteristics by coating noble metal materials such as Pd, Pt, Au, and Ag having high catalytic reaction characteristics and high work function, To extend the surface depletion layer to maximize a change in electrical resistance (Japanese Patent Application Laid-Open No. 10-2004-0043132).

Further, there is a method of coating the surface with another substance as a method for improving the detection characteristic. This method maximizes the electrical resistance by extending the depletion layer of the nanowire. It is generally known that the characteristic is maximized through the coating of the length of the Debye. Patent Document 10-2013-0104173 discloses a method for detecting a gas such as carbon monoxide, nitrogen dioxide, ethanol, hydrogen sulfide, hydrogen or the like singly or two or more at the same time, which is coated on the surface of a zinc-zinc tin nano- A zinc oxide tin oxide nanorod for a gas sensor comprising a palladium particle coating layer is disclosed. It has been reported that the improvement of the gas detection property by the coating of the bismuth oxide nanoparticles has not been reported yet. It has been reported that when the coating is applied to the zinc oxide nanorods, the photoluminescence property is increased or the photocatalytic effect is increased when the coating is applied to the titanium oxide nanotubes .

Among various MOS materials, indium oxide has been studied as a gas detection sensor. Various researches have been conducted on the detection reaction characteristics of hydrogen, carbon monoxide, nitrogen dioxide, ozone, and chlorine. Particularly, intensive researches and reports on the detection characteristics of ethanol gas have been made. This material exhibits a very high detection characteristic for ethanol gas compared to other materials and may exhibit a characteristic that the performance improvement is maximized through post-processing such as coating or doping. Therefore, it has been reported that very high reactivity and improvement of gas selectivity have been reported in the studies of synthesizing ultrafine oxide indium nanomaterials and coating them with platinum or lanthanum oxide nanoparticles.

However, even in the case of such an indium oxide nanomaterial, the thin film sensor element may have a limitation in the detection characteristic. Since the surface area of a thin film material is the same as a general bulk material even if it is a nanomaterial, the adsorption area of the gas is not high in the gas detection reaction. In general, a thin film type indium oxide sensor must be heated to about 200 to 600 DEG C for the gas detection reaction, and such a high temperature condition is a very unfavorable condition for the stability of the device. Particularly, indium oxide has unstable properties at high temperatures, and thus can not be used for a long time at a temperature of about 600 ° C.

On the other hand, nanomaterials with a one-dimensional structure are advantageous in solving these drawbacks. The types of nanomaterials can be classified into nanorods, nanowires, nanofibers, nano-needles, and the like depending on their types. Such a structure material is advantageous in forming a current channel when fabricating the device in one dimension, which is very advantageous for manufacturing a device such as a gas detection device. The one-dimensional structure of indium oxide nanomaterial can be synthesized by the following method. These methods include chemical vapor deposition (CVD), electrospinning, sol-gel method, and hydrothermal synthesis.

There are several methods for coating the noble metal to improve the gas detection performance of this material. In order to coat the Pt nanoparticles, the synthesized nanomaterials were mixed with a certain concentration of H ₂ PtCl ₆ Is added to an aqueous solution, and then heated. Also, p-aminophenyl trimethoxysilane is used to coat Au nanoparticles. In addition to this method, the noble metal is coated on the surface of the indium oxide nanomaterial synthesized by various methods to coat the noble metal nanoparticles by a sputtering method to a thickness of several to several tens nm, and then heat treatment is performed in an Ar atmosphere at 800 ° C. or more for 30 minutes or more There is a way. However, the synthetic method using such a few step method may cause crystals to be deformed or damaged in the heat treatment step during the synthesis process. In particular, since indium oxide is a weak oxide in heat, such a heat treatment may cause a serious problem to the stability of the device. In addition, the increase in the process cost and the increase in the time that occur during each step serve as a disadvantage in commercialization.

In the present invention, bismuth oxide, which is a p-type material, is coated on the surface of an n-type material indium oxide to form p / n bonds between the two materials through a single process. The low concentration of ethanol gas is effectively detected at a low temperature Indium oxide nanorods coated with bismuth oxide nanoparticles were prepared.

Patent Document 1: Patent Document 10-2013-0104173

An object of the present invention is to provide a bismuth oxide-coated indium oxide nanorod and a method of manufacturing the same.

In order to achieve the above object, And a bismuth oxide nanoparticle coating layer coated on the surface of the nanorod; and a bismuth oxide coated nanoporous oxide layer for gas detection.

Further, the present invention relates to a method for manufacturing an indium oxide nanorod; And (b) forming bismuth oxide nanoparticles on the surface of the indium oxide nanorods prepared in the step (1) (step 2). The present invention also provides a method for manufacturing a bismuth oxide-coated indium oxide nanorods for gas detection.

Further, the present invention relates to a substrate comprising: a substrate; Insulating layer; A bismuth oxide coated indium niobium rod for gas detection; And an electrode.

The bismuth oxide-coated indium oxide nanorods prepared through the present invention can be produced by using indium sulfide powder instead of indium or indium oxide powder which has been used in the prior art to produce nanorods having a small diameter, , The p / n junction composite nanorods can be synthesized without diffusion of a relative substance between indium oxide and bismuth oxide. Further, compared with the single structure nanomaterial, the gas detection performance can be improved due to the improvement of the catalytic properties of the substance, the gas adsorption at the interface, the increase of the potential barrier, and the increase of the depletion layer. In particular, A rod sensor can be manufactured.

FIG. 1 is a photograph of a bismuth oxide-coated indium oxide nanodevice according to the present invention observed with a scanning electron microscope; FIG.
2 is a graph showing X-ray diffraction analysis of bismuth oxide-coated indium oxide nanorods according to the present invention;
FIG. 3 is a photograph of a bismuth oxide-coated indium oxide nanorods according to the present invention observed with a transmission electron microscope; FIG.
FIG. 4 is a photograph and a photograph of a component of the bismuth oxide-coated indium niobium oxide according to the present invention observed by a transmission electron microscope; FIG.
FIG. 5 is a graph illustrating an ethanol gas detection reaction characteristic of the bismuth oxide-coated indium oxide nanorods according to the present invention;
6 is a graph showing the rate of ethanol gas detection and recovery in the bismuth oxide-coated indium oxide nanorods according to the present invention;
7 is a graph showing the gas detection characteristics of the indium oxide nanorods according to the ratio of the coated bismuth oxide;
8 is a graph showing the gas detection reaction values of the bismuth oxide coated indium oxide nanorods according to the present invention;
9 is a graph showing the gas detection reaction value according to the supply of the volatile organic compound gas to the bismuth oxide coated indium oxide nanorods according to the present invention;
FIG. 10 is a graph illustrating electrical characteristics of an indium oxide nanodevice coated with bismuth oxide coated with ethanol or air according to the present invention; FIG.
FIG. 11 is a graph showing energy band diagrams of bismuth oxide-coated indium oxide nanorods according to the present invention and changes in charge carriers and depletion layers generated in nanorods. FIG.

The present invention relates to an indium oxide nanorod; And a bismuth oxide nanoparticle coating layer coated on the surface of the nanorod; and a bismuth oxide coated nanoporous oxide layer for gas detection.

The indium oxide nanorods can be manufactured using indium sulfide powder, which is not indium or indium oxide, and thus nanorods of a thin thickness and a diameter can be manufactured. The bismuth oxide nanoparticle coating layer coated on the surface of the indium niobium oxide rod is preferably formed using a raw material in which a bismuth powder and an indium sulfide powder are mixed. The bismuth powder is preferably contained in an amount of 10 to 40 parts by weight based on 100 parts by weight of the mixed raw material, but is not limited thereto.

The optimum temperature for the gas detection of the bismuth oxide coated bismuth oxide nanorods according to the present invention is in the range of 150 to 250 ° C. Since the ion adsorption layer on the nanorod surface is sufficiently activated at a lower temperature than the existing technology, Adsorption to the nanorod surface becomes active. Also, since the reaction between oxygen ions and ethanol occurs actively during the supply of ethanol gas, the desorption of oxygen ions by the reaction with ethanol increases, so that even if ethanol of the same concentration is supplied, the resistance change becomes larger.

On the other hand, one-dimensional nanomaterials such as nanorods, nanowires, and nanotubes basically have very small diameters. When a semiconductor material is ionized and adsorbed on the surface, electrons are released or adsorbed to change the electrical characteristics. This effect is caused by the thickness of the Debye from the surface. Therefore, when a nanomaterial using a metal oxide is exposed to air, it adsorbs oxygen and ionizes. At this time, electrons are adsorbed and electrons on the surface of the nanomaterial are adsorbed. Since n-type semiconductors are materials that use electrons as charge carriers, a depletion layer is formed on the surface in this case. Since the thickness of the depletion layer is equal to the Debye length, it is important that the diameters of the synthesized nanomaterials are twice as large as the Debye length in order to exhibit optimal gas detection characteristics using the one-dimensional nanomaterials . If the diameter of the nanomaterial is longer than twice the length of the Debye, the nanomaterial is not completely insulated even when exposed to air and the center of the nanomaterial acts as a conductive path, so that the resistance increase is not maximized, . On the other hand, when the diameter is smaller than twice the length of the Debye, the depletion layer is overlapped, so that it does not respond to the detection of the low concentration gas, and the detection efficiency becomes low.

FIG. 10 is a diagram showing the above contents. In the case of nanorods with the optimum thickness, when the nanorods are exposed to air, they are completely insulated to maximize the resistance. After that, a reducing gas such as ethanol is supplied to bind the oxygen ions and desorb the oxygen ions on the surface of the nanorods. Is again supplied into the nanorods and the thickness of the insulating layer of the nanorods is reduced. Therefore, in this case, since the conductive path at the center of the nanorod is generated, the resistance is reduced and the gas detection characteristic can be measured using this difference.

Further, the present invention relates to a method for producing an indium oxide nanorod; And (b) forming bismuth oxide nanoparticles on the surface of the indium oxide nanorods prepared in the step (1) (step 2). The present invention also provides a method for manufacturing a bismuth oxide-coated indium oxide nanorods for gas detection.

Hereinafter, a method for manufacturing a bismuth oxide-coated indium oxide nanorods for gas detection according to the present invention will be described in detail.

In the method for producing the bismuth oxide coated oxide indium nanorods for gas detection according to the present invention, Step 1 is a step of producing the indium oxide nanorods.

The process of step 1 is preferably carried out using an indium sulfide powder, but is not limited thereto. In the conventional process technology, indium or indium oxide powder was mainly used, but since the thickness of the prepared nanomaterial was thick, Mg and the like were added. However, there is a problem that impurities may be mixed when they are prepared by adding Mg or the like. In the method for producing the indium oxide nanorods coated with bismuth oxide according to the present invention, nanorods of thin thickness and diameter are manufactured by using indium sulfide powder which is not indium or indium oxide powder in the production of the indium oxide nanorods .

The production of the indium oxide nanodevice of the step 1 may be performed by at least one method selected from the group including Vapor-Liquid-Solid (VLS), hydrothermal synthesis and electrospinning, but is not limited thereto. The vapor-liquid-solid (VLS) method is a method in which a vapor-phase indium-containing paper carried in a high-temperature furnace is condensed on the surface of a molten catalyst such as gold and crystallized to grow into an indium oxide nanorod. Specifically, a silicon wafer coated with a gold thin film as a catalytic material and indium sulfide are placed in a reactor and heated to a high temperature to convert the indium sulfide into a gas phase to adhere to the surface of the gold thin film, and a gold- After the droplet is formed, the nanorods grow in one direction from the solid-liquid boundary by the gas supplied. And the breakdown of the symmetry at the solid-liquid interface by the supplied reaction gas is an important step in the formation of one-dimensional nanocrystals in the VLS method. In addition, since the mixed solution droplet of the catalyst and the reaction gas acts as a template in manufacturing nanorods, it is possible to control the diameter of the synthesized nanorod according to the size of the catalyst particles. The length of the nanorod is proportional to the reaction time, so the length of the nanorod is also controllable.

It is preferable that a mixed gas of an oxidizing gas or a divalent inert gas is supplied to the step of the step 1. The inert gas that can be supplied at this time may be argon (Ar), nitrogen (N ₂ ), helium (He), or hydrogen (H ₂ ), but is not limited thereto. It is preferable that oxygen (O ₂ ) is supplied as the oxidizing gas, and the mixed concentration of oxygen can be supplied at a constant concentration of 0.1 to 10% with respect to the supplied gas. The pressure inside the reactor may be kept constant at 0.5 to 10 torr in the step 1, but is not limited thereto. Further, the reaction time of the production of the indium oxide nanorods can be maintained for 30 minutes to 2 hours, but is not limited thereto.

In the method for producing bismuth oxide coated oxide indium nanorods for gas detection according to the present invention, step 2 is a step of forming bismuth oxide nanoparticles on the surface of the indium oxide nanorods prepared in step 1 above.

The step 2 is preferably carried out using a raw material in which a bismuth powder and an indium sulfide powder are mixed. The bismuth powder is preferably contained in an amount of 10 to 40 parts by weight based on 100 parts by weight of the mixed raw material, but is not limited thereto. If bismuth powder is contained in an amount of less than 10 parts by weight based on 100 parts by weight of the mixed raw material, there may be a problem that bismuth oxide nanoparticles are not formed on the surface of the indium oxide nano rod, The bismuth oxide nanoparticles formed on the surface of the indium oxide nanorod are aggregated into a lump shape rather than a particle shape, or the lump clusters cover the surface of the nanorod rod to prevent contact between the nanorod and the gas, and finally, There may arise a problem that bismuth oxide nanorods are formed instead of bismuth oxide nanoparticles formed on the indium oxide nanorods.

When the bismuth powder is mixed in an appropriate amount, nanostructures of a composite structure can be produced. Since diffusion into a relative material is not achieved between indium oxide and bismuth oxide, bismuth oxide, which is a p-type material, P / n-bonded composite nanorods formed by p / n bonding between the two materials can be manufactured by coating the surface of indium oxide.

In addition, the step 2 may be performed by a Vapor-Liquid-Solid (VLS) method. In the vapor-liquid-solid (VLS) method, the vapor-phase bismuth powder and the indium sulfide powder mixed in a high-temperature furnace are condensed on the surface of the indium oxide nanodevice so as to crystallize the bismuth oxide- And grown to an indium oxide nanorod.

The method for producing bismuth oxide-coated indium oxide nanorods for gas detection according to the present invention is characterized in that bismuth oxide for detecting at least one gas selected from the group consisting of ethanol, methanol, acetone, benzene and toluene is coated The indium oxide nanorods can be produced. At this time, it is not limited to the gas.

The detection of ethanol gas using nanorods is measured by the resistance change of the nanorods depending on the presence or absence of oxygen ions adsorbed on the nanorod surface. Therefore, it is important to analyze the oxygen adsorption on the surface of the nanorods. At low temperatures, the adsorption layer of ions existing on the nanorod surface is scarcely activated. Therefore, even if the nanorods are exposed to air in this case, the nanorods will not adsorb oxygen, and the depletion layer on the nanorod surface will hardly be produced. Also, even if ethanol gas is supplied in this situation, not only the reaction of oxygen ions and ethanol does not actively take place but also the overall resistance change becomes small as the amount of adsorbed oxygen ions is small. On the other hand, at the optimal temperature, since the ion adsorption layer on the nanorod surface is sufficiently activated, the ionization of oxygen causes the adsorption to the surface of the nanorods actively. Also, since the reaction between oxygen ions and ethanol occurs actively during the supply of ethanol gas, the desorption of oxygen ions by the reaction with ethanol increases, so that even if ethanol of the same concentration is supplied, the resistance change becomes larger. On the other hand, if the temperature is too high, the charge carrier concentration of the nanorod increases sharply. In this case, the oxygen ions adsorbed on the surface of the nanorod are too strongly bound to be desorbed by the reaction with ethanol, and the depletion layer decreases due to the increased charge carrier, so that the depletion layer Will disappear. Therefore, even if ethanol is supplied, the resistance does not change greatly. The optimum temperature for gas detection of the bismuth oxide-coated indium oxide nanorods according to the present invention is preferably 150 to 250 ° C, but is not limited thereto. The bismuth oxide nanoparticles present on the surface of the indium oxide nanorods act as a catalyst for the adsorption of oxygen and the oxidation of ethanol, so that the optimal detection reaction temperature can be somewhat lowered compared with the existing technology.

Indium oxide is a material that exhibits excellent catalytic properties for ethanol oxidation, and is generally a substance specialized in ethanol gas detection. However, metal oxide based gas sensors generally have a disadvantage in that the gas selectivity is poor, and indium oxide is also a metal oxide semiconductor material, which is not excellent in selectivity. On the other hand, as the bismuth oxide nanoparticles are formed on the surface of the indium oxide nanorods and act as a catalyst, the selectivity for each gas can be significantly increased.

On the other hand, in the case of metal oxide one-dimensional nanomaterials on which metal oxide semiconductor nanoparticles are formed on the surface, the gas detection is improved on a principle different from that of the noble metal nanoparticles formed on the surface. Unlike the noble metal nanoparticles, the change in the potential barrier due to the depletion layer generated at the interface and the change in the thickness of the depletion layer can improve the gas detection characteristics, although the catalytic reaction may be caused depending on the kind of the nanoparticles. In the bismuth oxide-coated oxide indium nanorods of the present invention, p-type nanoparticles are formed on the surface of the n-type nanorods, and a neutral depletion layer is formed on both sides of the interface. When the nanomaterial is exposed to the air, it adsorbs oxygen in the air and changes into oxygen ions to adsorb electrons on the surfaces of the nanorods and the nanoparticles. Oxygen in the air adsorbs on the nanorods and reacts as shown in the following reaction formulas 1 to 3 and absorbs electrons as charge carriers to form a depletion layer.

<Reaction Scheme 1>

O ₂ (g) + e ^- ? O ₂ ^- (ad)

<Reaction Scheme 2>

1/2 O ₂ (g) + e ^{- -} O ^- (ad)

<Reaction Scheme 3>

O ^- (ad) + e ^- &gt; O ^2- (ad)

Further, when adsorbed on the nanoparticles, the reaction shown in the following Reaction Schemes 4 to 6 is performed, and holes serving as charge carriers are produced.

<Reaction Scheme 4>

O ₂ (g) O ₂ ^- (ad) + h ⁺

<Reaction Scheme 5>

_{1/2 O 2 (g) → O} - (ad) + h +

<Reaction Scheme 6>

O- (ad) ^- &gt; O ^2- (ad) + h ⁺

When the ethanol gas is supplied, the oxygen ions on the surfaces of the nanorods react with the ethanol gas as shown in the following equations (7) and (8).

<Reaction Scheme 7>

C ₂ H ₅ OH (g) + O ^2- (ad) CH ₃ CHO (g) + H ₂ O (g) + 2e ^-

<Reaction Scheme 8>

CH ₃ (g) + 5 O ^2- (ad) 2 CO ₂ (g) + 2 H ₂ O (g) + 10 e ^-

On the surface of the nanoparticles, the reactions shown in the following Reaction Schemes 9 and 10 are shown.

<Reaction Scheme 9>

C ₂ H ₅ OH (g) + O ^2- (ad) + 2 h ⁺ ? CH ₃ CHO (g) + H ₂ O (g)

<Reaction formula 10>

CH ₃ (g) + 5 O ^2- (ad) + 5 h ^{+ -} 2 CO ₂ (g) + 2 H ₂ O (g)

In this way, the oxygen ions adsorbed on the surface of the nanorod are removed, and the removed gas is discharged through the exhaust port. At the same time, when the electrons that have been adsorbed by the oxygen ions are released again and supplied to the inside of the nanorod, the depletion layer of the nanorod decreases sharply. Also, as electrons are supplied to the nanoparticles, the hole aggregation layer sharply decreases, and the depletion layer of the nanoparticles is expanded around the interface. This supply of electrons sharply lowers the potential barrier to free the charge carriers and reduces the thickness of the nanorod depletion layer to much less than the Debye length. As a result of this reaction, the increased resistance of the conductive passages inside the nanorods leads to a drastic reduction in resistance and gas detection.

Further, the present invention provides a semiconductor device comprising: a substrate; Insulating layer; A bismuth oxide coated indium niobium rod for gas detection; And an electrode.

In the gas sensor according to the present invention, it is preferable to use a semiconductor substrate, a conductive substrate, a nonconductive substrate, or the like. Specifically, the semiconductor substrate may be a silicon substrate, a Group III-V semiconductor substrate or the like, and the conductive substrate may be a metal substrate, a conductive organic compound substrate, or the like. The nonconductive substrate may be a glass substrate, Can be used. However, since the silicon substrate of the semiconductor substrate has good recoverability and low current consumption, it is more preferable to use a silicon substrate in manufacturing the gas sensor of the present invention.

Further, the insulating layer is positioned below the bismuth oxide coated indium oxide nanorods and two or more kinds of electrodes. The insulating layer serves to electrically isolate the bismuth oxide coated indium oxide nanorods and two or more electrodes from the substrate. The insulating layer may be made of silicon dioxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), tantalum oxide (Ta ₂ O ₅ ), zirconium oxide (ZrO ₂ ), hafnium dioxide (HfO ₂ ) a silicon nitride oxide film and the oxide, or the like titanium dioxide (TiO ₂₎ (SiON), silicon nitride (Si ₃ N ₄₎ such as a nitride film or a hafnium silicon oxynitride (HfSiON), hafnium silicate (HfSi _X O _Y, including, where 0.1 <X < 9 and 2 < Y < 4), and the like is preferably used. More preferably, silicon dioxide having thermal stability is used.

The gas sensor may detect at least one gas selected from the group consisting of ethanol, methanol, acetone, benzene, and toluene, but is not limited thereto. The detection of ethanol gas using nanorods is measured by the resistance change of the nanorods depending on the presence or absence of oxygen ions adsorbed on the nanorod surface. At the optimum temperature, the ion adsorption layer on the nanorod surface is sufficiently activated, so oxygen is ionized and adsorption to the nanorod surface becomes active. Also, since the reaction between oxygen ions and ethanol occurs actively during the supply of ethanol gas, the desorption of oxygen ions by the reaction with ethanol increases, so that the resistance change becomes large even if the same concentration of ethanol is supplied.

Hereinafter, the present invention will be described in more detail with reference to examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

Example 1 Production of bismuth oxide-coated indium oxide nanorods

Step 1: A 3 nm Au thin film was coated on the surface of the Si wafer using a DC sputter, and then the indium sulfide powder was charged into the crucible. Then, the substrate was placed on the substrate with the coated side facing downward. At this time, the distance between the substrate and the powder was maintained at 10 mm or less.

Step 2: The crucible of step 1 was charged into the quartz tube horizontal tubular furnace, and the furnace was sealed. Then, the inside of the furnace was evacuated and heated to 800 占 폚 while maintaining a heating rate of 10 占 폚 / min.

Step 3: An inert gas such as N ₂ or Ar was supplied to the carrier gas and O ₂ was supplied as the oxidizing gas. Each gas was controlled by MFC (Mass Flow Controller) and the concentration of oxygen was maintained at 2%. In addition, the pressure inside the furnace was maintained at 1 Torr to prepare indium oxide nanorods for 1 hour.

Step 4: After the production of step 3 was completed, the supply of the gas was stopped, the vacuum was maintained, and after cooling to room temperature, the vacuum was removed.

Step 5: A mixed powder of a bismuth powder and an indium sulfide powder having a weight ratio of 20 to the mixed powder, using a vapor-liquid-solid (VLS) method, was applied to the surface of the indium oxide- To prepare a bismuth oxide-coated indium oxide nanorods.

&Lt; Example 2 > Production of gas sensor

Step 1: An IDE (Interdigital Electrode) type FET device using the nanorods of the first embodiment as a channel was fabricated. At this time, the IDE chip was fabricated on a Si / SiO ₂ (SiO ₂ : 300 nm) wafer substrate through photolithography, and the distance between the source and the drain was made to be 30 μm. The electrode layer was E-beam evaporated to Ti / Pt (10 nm / 100 nm) thickness. Each of the synthesized nanorods was prepared in an amount of 50 mg, and the nanorod powder was added to 5 ml of ethanol and ultrasonically stirred for 30 seconds.

Step 2: 1 ml of the stirred suspension of Step 1 was dropped on an IDE chip using a pipette, followed by coating at a speed of 300 rpm for 30 seconds, followed by drying at 150 ° C for 1 minute to perform spin coating. The above procedure was repeated five times so that the nano bars on the surface of the IDE chip were connected between the electrodes in a multiple connection structure.

Step 3: The IDE chip manufactured in step 2 was mounted on the gas detection device. The chamber equipped with the chip was in the form of a quartz tube horizontal tube, sealed and sealed off from the outside. However, a gas tube was installed, the end of the tube was positioned 5 mm in front of the IDE chip, and a gas tube of 1 inch in diameter was provided on the opposite side of the gas injection tube to manufacture a gas sensor.

&Lt; Comparative Example 1 &

The indium niobium oxide coated with bismuth oxide was prepared in the same manner as in Example 1 except that only the indium sulfide powder was coated without the bismuth powder in the step 5 of Example 1.

<Experimental Example 1> The shape of the bismuth oxide-coated indium oxide nanorods

In order to understand the shape of the bismuth oxide-coated indium oxide nanorods of Example 1, the results of observation with a scanning electron microscope (SEM, Hitach S4200) are shown in Fig.

As shown in FIG. 1, FIG. 1 (a) is a photograph of the nanorods magnified at 20,000 magnifications, and FIG. 1 (b) shows a photograph of the nanorods magnified to 200,000 magnifications . In FIG. 1 (a), the synthesized nanomaterial is synthesized as a rod and exhibits a very high aspect ratio. In (b), the nanorod is synthesized into a rectangular shape and a projection is formed on the surface can confirm. It can be assumed that the cause of the projections is attributed to the bismuth powder mixed in the raw material powder. Accordingly, the nanorods of the present invention have a high aspect ratio and include bismuth as protrusions, thereby increasing the surface area of the nanorods, thereby improving the effect of the gas sensor including the nanorods.

<Experimental Example 2> Characteristic analysis of bismuth oxide-coated indium oxide nanorods

In order to understand the determination of properties of the nanorods grown in Example 1 were analyzed by X- ray diffraction (XRD, X-ray Diffractometer, Phillips X'pert MRD Pro), to measure a thin film material, 0.5 ^o The angle analysis was performed with a 2θ analysis with a low angle corner. In addition, a transmission electron microscope (Jeol 2100F) equipped with an energy dispersive X-ray spectroscopy (EDS) was performed to confirm the qualitative analysis and the crystallinity of the components of the nanorods. Through the above analysis, the components of the nanorods formed with the bismuth oxide nanoparticles of Example 1 and the nanorods of Comparative Example 1 were analyzed and their crystallizabilities were analyzed. The results are shown in FIGS. 2 to 4.

As shown in FIG. 2, indium oxide peaks strongly appear in both the nanorods formed with the bismuth oxide nanoparticles of Example 1 and the nanorods without the bismuth oxide nanoparticles of Comparative Example 1. On the other hand, it can be confirmed that a bismuth oxide peak is formed in the graph of nanorods in which the bismuth oxide nanoparticles of Example 1 are formed.

As shown in FIG. 3, FIGS. 3 (a) and 3 (d) are low-magnification TEM photographs. When the two photographs are compared, it can be seen that a protrusion is synthesized on the surface in (d). 3 (b) and 3 (e), high-resolution image photographs of the two types of nanorods were taken, and crystal lattice patterns of indium oxide can be confirmed. The pattern is relatively clear and the material synthesized through the interval of the lattice is indium oxide, and the protrusion formed on the surface is bismuth oxide. 3 (c) and 3 (f) show the diffraction gratings of indium oxide synthesized by a single crystal, while FIG. 3 (c) f) shows that a ring-shaped bismuth oxide diffraction pattern appears in addition to this diffraction pattern. Unlike a regular diffraction pattern of indium oxide, bismuth oxide appears as a ring in the form of a ring. In the case of bismuth oxide formed on the surface as a typical type of polycrystalline material, although one crystal of a nanoparticle is a single crystal, It can be explained that a pattern is formed by a polycrystalline ring. In addition, the ring pattern is very dark, as indium oxide is synthesized in large quantities with very good crystallinity, whereas in the case of bismuth oxide, the amount of the bismuth is relatively small in the ring pattern.

As shown in Fig. 4, Fig. 4 (a) is a scanning transmission electron microscope (STEM) photograph of Fig. 3 (d). The above photograph is a photograph for the EDS analysis. The EDS analysis is a photograph of the composition of the substance shown in the photograph. 4 (b) to 4 (d) are photographs of the EDS mapping analysis of FIG. 4 (a). The photographs show oxygen, indium, and bismuth, respectively, and show the distribution and the amount of each component. From this figure, it can be seen that the protruding part of the synthesized material is bismuth oxide nanoparticles, and the nanorods are made of indium oxide. In addition, it can be confirmed that bismuth is not generally doped in the nanorod portion and conversely, indium is not doped in the nanoparticle portion. However, since the resolution of qualitative analysis is not relatively high in EDS, it is difficult to grasp the exact degree of doping through this analysis.

Experimental Example 3 Detection characteristics of ethanol gas in bismuth oxide-coated indium oxide nanorods

In order to analyze the ethanol gas detection characteristics of the indium oxide nanorods coated with the bismuth oxide oxide of Example 1 and the indium oxide nanorods not coated with the bismuth oxide of Comparative Example 1, the following experiment was conducted.

A quartz horizontal tubular furnace was used as a chamber, and a jacket type muffle furnace for heating the surface of the tubular furnace was used to control the temperature, and Yokogawa PID was used for temperature control. For the accurate temperature measurement, the temperature of the surface of the sensor chip and the temperature of the furnace were measured using a k-type thermocouple. The supply of gas was injected at 5mm from the front of the sensor, and exhaust pipe was installed at the rear to allow natural exhaust. For the gas supply, 200ppm ethanol gas and synthetic air diluted with synthetic air were prepared and the gas was supplied at each concentration by adjusting the ratio using MFC (KOFLOC-3660). Gas detection characteristics were measured using a source meter (Keithley, Model No. 2612) with electrodes connected to the sensor. Experiments were conducted on indium oxide nanorods coated with bismuth oxide of Example 1 at a temperature of 200 ° C and indium oxide nanorods not coated with bismuth oxide of Comparative Example 1 as shown in FIGS. 5 (a) and 5 b). 5 (c) shows the result of measuring the resistance at 90% of the resistance change value and showing the value of Ra / Rg * 100 (%). Based on the values shown in Figs. 5 (a) and 5 (b), when the target gas was supplied, the time measured at 90% of the resistance change and the 90% A graph showing the measured time is shown in Fig.

As shown in FIG. 5, the analysis of the graph shows that the detection reaction is very fast in each concentration reaction, while the recovery reaction is somewhat slow. As shown in Figs. 6 (a) and 6 (b), it can be seen that the difference in the velocity according to the concentration is not large. This is because the oxygen on the nanorod surface reacts with the ethanol on the surface of the nanorod via the chemical reaction, and the oxygen ion on the surface is desorbed at a high rate. However, once the desorbed oxygen has supplied the recovery gas, it is difficult to be adsorbed again. It can be assumed that it takes a long time to completely discharge the ethanol gas present between the fuel cell and the fuel cell. The base resistance of Example 1 was higher than that of Comparative Example 1, and the resistance change in the detection reaction was also larger than that of Example 1. The difference becomes larger as the concentration of ethanol to be detected is higher, which can be confirmed through FIG. 5 (c). As shown in this graph, when the concentration of ethanol is 10 ppm, there is almost no difference in detection characteristics between the two sensors. On the other hand, when the concentration is higher than 20 ppm, the difference of the detection characteristics begins to increase, and the difference is seen to increase rapidly as the concentration increases. This is presumably because, in the case of the low concentration, the resistance change is small and the target gas to be detected is very small, so that the reaction itself does not occur well.

6 (a) and (b), the reaction and the recovery rate were analyzed. As a result, the reaction and the reaction rate of Comparative Example 1 were found to be about 13 seconds and about 350 seconds, respectively. In Example 1 It can be seen that it appears around 24 seconds and 190 seconds respectively. In the case of Comparative Example 1, although the reaction rate was fast, the recovery rate was slow and the difference was about 30 times, whereas in Example 1, the difference was 8 times or less. Also, the rate of reaction was faster for Comparative Example 1, while the rate of recovery was much faster for Example 1. This can be attributed to the influence of the bismuth oxide nanoparticles. Oxygen is easily adsorbed on the surface of the nanomaterial due to the catalytic function of the substance, and adsorbed electrostatically, while adsorbed oxygen is desorbed It can be explained that it is difficult to be. The gas detection reaction time of the indium oxide is very fast, which is on the order of 10 to 20 seconds, but consumes hundreds of seconds for recovery. Therefore, the somewhat slower reaction time does not have much meaning, but the reduction of recovery time is a big advantage.

<Experimental Example 4> Characteristics of bismuth oxide-coated indium oxide nanorods

In step 5 of Example 1, nanoporous rods were synthesized using raw powders having a weight ratio of bismuth powder of 0, 10, 20, 30, and 40 to the mixed powder, and 200 ppm of ethanol gas detection characteristics And analyzed through the following experiment.

A quartz horizontal tubular furnace was used as a chamber, and a jacket type muffle furnace for heating the surface of the tubular furnace was used to control the temperature, and Yokogawa PID was used for temperature control. For the accurate temperature measurement, the temperature of the surface of the sensor chip and the temperature of the furnace were measured using a k-type thermocouple. The supply of gas was injected at 5mm from the front of the sensor, and exhaust pipe was installed at the rear to allow natural exhaust. For the gas supply, 200ppm ethanol gas and synthetic air diluted with synthetic air were prepared and the gas was supplied at each concentration by adjusting the ratio using MFC (KOFLOC-3660). Gas detection characteristics were measured using a source meter (Keithley, Model No. 2612) with electrodes connected to the sensor. Each sensor of the nanorods was mounted on the device and 200 ppm of gas was supplied at a temperature of 200 ° C to measure the detection characteristics. A voltage of 1 V was applied to each measurement, FIG. 7 shows the resultant graph obtained by measuring the number of times. Among the nanorods, 200 ppm ethanol gas was supplied to the nanorods using bismuth powder and raw material powder having a weight ratio of 0 and 20 to the mixed powder, 8.

As shown in FIG. 7, the data of the graph is calculated by calculating the reaction value, not the resistance value, for the intuitive comparison of the result value, and the reaction value varies according to the sample in the upper right part of the graph. As a result, it was found that the ethanol gas detection characteristic of Example 1 was the most excellent.

As shown in FIG. 8, in the case of the nanodevice without the bismuth oxide coating of Comparative Example 1, the optimal detection characteristics were shown at 250 ° C., whereas in the case of the nanodevice coated with the bismuth oxide of Example 1, It was confirmed that the highest reaction value was obtained at 200 ° C, which is 50 ° C lower. In addition, Example 1 exhibited a higher reaction value than Comparative Example 1 at all temperatures, indicating that the gas detection performance of Example 1 was better regardless of the temperature. The detection of ethanol gas using nanorods is measured by the resistance change of the nanorods depending on the presence or absence of oxygen ions adsorbed on the nanorod surface. Therefore, it is important to analyze the oxygen adsorption on the surface of the nanorods. At low temperatures, the adsorption layer of ions existing on the nanorod surface is scarcely activated. Therefore, even if the nanorods are exposed to air in this case, the nanorods will not adsorb oxygen, and the depletion layer on the nanorod surface will hardly be produced. Also, even if ethanol gas is supplied in this situation, not only the reaction of oxygen ions and ethanol does not actively take place but also the overall resistance change becomes small as the amount of adsorbed oxygen ions is small. On the other hand, at the optimal temperature, since the ion adsorption layer on the nanorod surface is sufficiently activated, the ionization of oxygen causes the adsorption to the surface of the nanorods actively. Also, since the reaction of oxygen ions with ethanol during the supply of the ethanol target gas is also active, the desorption of oxygen ions due to the reaction with ethanol increases, so that the resistance change becomes larger even if the same concentration of ethanol is supplied. On the other hand, if the temperature is too high, the charge carrier concentration of the nanorod increases sharply. In this case, the oxygen ions adsorbed on the surface of the nanorod are too strongly bound to be desorbed by the reaction with ethanol, and the depletion layer decreases due to the increased charge carrier, so that the depletion layer Will disappear. Therefore, even if ethanol is supplied, the resistance change does not change significantly. Therefore, it is important to find the optimal temperature for gas detection, and it can be seen that the temperature that gives the best results in two kinds of sensors is somewhat different. This can be attributed to the presence of bismuth oxide nanoparticles on the surface of the nanorods, and it can be expected that the bismuth oxide acts as a catalyst for oxygen adsorption and ethanol oxidation, resulting in a somewhat lower optimal detection reaction temperature.

Experimental Example 5: Selectivity of bismuth oxide-coated indium oxide nanorods by gas

In order to show the selectivity of each of the indium oxide nanorods coated with the bismuth oxide-containing oxide of Example 1 and the indium oxide nanorods not coated with the bismuth oxide oxide of Comparative Example 1, 200 ppm of each of the other volatile organic compounds FIG. 9 is a graph showing a gas detection reaction value when the gas is supplied.

As shown in FIG. 9, the detection characteristics of five kinds of VOC (Volatile Organic Compound) gases including ethanol were measured. As a result, the bismuth oxide-coated indium oxide nanorods of Example 1 exhibited the highest detection response characteristics in ethanol and relatively low detection characteristics in other gases, thereby confirming greatly improved detection performance in ethanol gas have. On the other hand, the indium oxide indium nano bar having no bismuth oxide coating of Comparative Example 1 showed that the selectivity to other gases including ethanol was not significantly different, and the detection performance against ethanol gas was lower than that of Example 1 of the present invention Can be confirmed. Therefore, in the case of the indium niobium oxide coated with bismuth oxide of Example 1, the catalyst characteristic for the ethanol oxidation reaction is most active at a temperature of 200 ° C, so that the detection characteristic of the ethanol gas is the most excellent.

<Experimental Example 6>

An energy diagram of the junction structure in which the bismuth oxide nanoparticles are formed on the surface of the indium oxide nanorods of Example 1 and a graph of the change of the charge carrier and the depletion layer formed in the nanorod are shown in FIG.

As shown in FIG. 11, electrons are released by the oxygen adsorbed on the surface of the indium oxide nanorods of Example 1, and a depletion layer is formed on the surface of the indium oxide nanorod, which is an n-type semiconductor. On the other hand, Because the nanoparticles use holes as charge carriers, the charge carriers will flocculate. As a result, electrons are more absorbed from the surface of the nanorod, and as shown in FIG. 11 (b), a depletion layer which is thicker than the length of the Debye is generated inside the nanorod around the nanoparticle, And it can be confirmed that the resistance is increased as a result.

Claims (11)

delete Preparing an indium oxide nanorod (step 1); And
(Step 2) of forming bismuth oxide nanoparticles on the surface of the indium oxide nanorods prepared in the step 1,
Wherein the step of the step 1 is carried out using an indium sulfide powder. 2. A method for manufacturing a bismuth oxide-coated indium oxide nanorod, comprising the steps of:
delete The method according to claim 2, wherein the step (1) of the indium oxide nanorods is carried out by at least one method selected from the group consisting of a Vapor-Liquid-Solid (VLS) method, a hydrothermal synthesis method and an electrospinning method Coated bismuth oxide nanostructures for gas detection.
[3] The method according to claim 2, wherein a mixed gas of an oxidizing gas or a divalent inert gas is supplied to the step 1).
3. The method according to claim 2, wherein the step (2) is carried out using a raw material in which a bismuth powder and an indium sulfide powder are mixed.
[7] The method of claim 6, wherein the bismuth powder is included in an amount of 10 to 40 parts by weight based on 100 parts by weight of the mixed raw material.
3. The method of claim 2, wherein the step (2) is performed by a Vapor-Liquid-Solid (VLS) method.
3. The gas detection method according to claim 2, wherein the gas detection is for detecting at least one gas selected from the group consisting of ethanol, methanol, acetone, benzene and toluene. Method of manufacturing nanorods.
Preparing an indium oxide nanorod using an indium sulfide powder (step 1); And
And a step (b) of forming the bismuth oxide nanoparticles on the surface of the indium oxide nanorod formed in the step (1), wherein the bismuth oxide nanorod is coated with bismuth oxide.
The gas sensor according to claim 10, wherein the gas sensor manufactured by the method of manufacturing the gas sensor detects at least one gas selected from the group consisting of ethanol, methanol, acetone, benzene and toluene. Way.

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