KR101621021B1 - Sensor having core-shell nanowire and preparing method of the same - Google Patents

Abstract

The present invention provides a sensor including a core-shell nanowire, comprising: a substrate; a core-shell nanowire including a core including a first metal oxide formed on the substrate and a shell including a second metal oxide; and an electrode layer formed on the core-shell nanowire, wherein a thickness of the shell of the nanowire is 1.1 to 2.9 times a Debye length. The core-shell nanowire manufactured according to the present invention exhibits gas detection characteristics beyond a limit of gas detection characteristics of an existing nanowire and an optimal thickness for determining a thickness of a shell can be found in manufacturing an optimal coating layer and core-shell structure.

Description

[0001] The present invention relates to a sensor having a core-shell nanowire and a method of manufacturing the core-

The present invention relates to a sensor comprising a core-shell nanowire and a method of manufacturing the same.

In recent years, sensors based on one-dimensional nanostructures have attracted much attention due to their high reactivity and detection speed compared to conventional sensors. One-dimensional nanostructured materials exhibit this property because of the high volume-to-surface area of the nanostructured material and the energy barrier in the overlapped portion when the one-dimensional materials are coupled together.

Numerous studies related to the one-dimensional nanostructured material have been conducted for the above reasons, and various studies for further improving the gas detection characteristics of the material have been continuously carried out. Sensitivity and reactivity of the gas detection sensor, selectivity, and limit of detectable gas concentration are some of the characteristics that the sensitivity of existing sensors should be further improved. In addition, as a method of processing the one-dimensional nanostructure to improve the above-mentioned characteristics, there are a method of deforming the shape, a core-shell structure, a metal functionalization and the like. The effect of improving the characteristics of the detection sensor can be expected.

Of the above methods, based on the core-shell structure, the Singh group studied the gas detection characteristics of the core-shell structure among the one-dimensional nanostructures (Sens. Actuators, B 2011, 160, 1346.1351). Specifically, it has been claimed that a depletion layer is formed at the core-shell interface between indium oxide and zinc oxide when a nanowire composed of indium oxide core and zinc oxide shell is supplied to the surface of the nanostructure, Shells are composed of different materials and have different work functions.

In addition, in the above study, no optimal shell thickness has been disclosed in the core-shell nanowire sensor, but the influence of the depletion layer at the core-shell interface and the surface and the effect of depletion layer at the multi- And that the gas detection characteristic is shown by the energy barrier of FIG.

On the other hand, indium oxide (In ₂ O ₃ ) is an oxide semiconductor exhibiting n-type characteristics in general, and has a direct transition band gap of 3.55 to 3.75 eV. Indium oxide has been used for the detection of ozone, nitrogen dioxide, carbon monoxide and hydrogen, but limited research has been conducted on the detection of ethanol. . Generally, in the case of a pure oxide indium nanowire gas detection sensor, the reactivity is 300% or less at an ethanol concentration of 100 ppm or less. In addition, in the prior art, simple indium oxide shows that the selective reactivity to ethanol gas is not high, and reactivity to carbon monoxide or hydrogen is very high.

Accordingly, in the present invention, a sensor including a core-shell nanowire and a manufacturing method thereof have been developed while studying a method for improving the ethanol detection characteristic, and the present invention has been completed.

It is an object of the present invention to provide a sensor comprising a core-shell nanowire and a method of manufacturing the same.

In order to achieve the above object,

materials;

A core-shell nanowire comprising a core comprising a first metal oxide formed on the substrate and a shell comprising a second metal oxide; And

And an electrode layer on the core-shell nanowire,

Wherein the thickness of the shell of the nanowire is 1.1 to 2.9 times the Debye length. The present invention also provides a sensor comprising the core-shell nanowire.

Further, according to the present invention,

Forming a core comprising a first metal oxide on a substrate (step 1);

Forming a sensing portion including the core-shell nanowire by forming a shell including a second metal oxide on the core (Step 2); And

And forming an electrode layer on the sensing unit (step 3)

Wherein the thickness of the shell is 1.1 to 2.9 times the length of the device.

The core-shell nanowire fabricated according to the present invention exhibits detection characteristics that are above the limits of conventional nanowire or gas detection capabilities and is optimized for optimal thicknesses of the shell layer in the fabrication of the core shell structure The thickness can be determined.

In addition, the core-shell nanowire included in the sensor according to the present invention has a shell thickness of 1.1 to 2 times the length of the shell device, so that the core-shell nanowire having improved sensitivity to a nanostructure or alloy nanostructure composed of a single material There are advantages.

FIG. 1 is a photograph of the indium oxide / zinc oxide nanowire prepared in Example 1 through a scanning electron microscope; FIG.
2 (a) and 2 (b) are photographs of the indium oxide / zinc oxide nanowire produced in Example 1 through a transmission electron microscope, and FIG. 2 (c) Area Electron Diffraction);
3 is a graph showing X-ray diffraction analysis of the indium oxide / zinc oxide nanowire prepared in Example 1;
FIG. 4 is a graph showing changes in the ethanol detection reaction characteristics of the sensor including the indium oxide / zinc oxide nanowire fabricated in Example 2 according to the thickness of the shell; FIG.
5 is a graph showing the ethanol detection reaction characteristics of the sensor including the simple synthesized indium oxide nanowire manufactured in Comparative Example 2 and the sensor including the indium oxide / zinc oxide nanowire fabricated in Example 2;
Figs. 6 (a) and 6 (b) are schematic diagrams showing energy band diagrams in a state of post-equilibrium bonding between the zinc oxide and the indium oxide.

Hereinafter, the present invention will be described in detail.

According to the present invention,

materials;

A core-shell nanowire comprising a core comprising a first metal oxide formed on the substrate and a shell comprising a second metal oxide; And

And an electrode layer on the core-shell nanowire,

Wherein the thickness of the shell of the nanowire is 1.1 to 2.9 times the Debye length. The present invention also provides a sensor comprising the core-shell nanowire.

Sensitivity, speed, selectivity, and limit of the detectable gas concentration of the gas detection sensor, which are intended to further improve the sensitivity of the existing sensor, include a one-dimensional As a method of processing the nanostructure, there are methods such as shape modification, core-shell structure, and metal functionalization. In the present invention, a nanowire having a core-shell structure and a gas detection sensor including the nanowire are manufactured from the above methods. When the thickness of the shell is 1.1 to 2 times the length of the shell, the nanowire is compared with the nanostructure or alloy nanostructure composed of a single material. And exhibited improved sensitivity.

Hereinafter, the sensor including the core-shell nanowire according to the present invention will be described in detail.

In the sensor comprising the core-shell nanowire according to the present invention, the first metal oxide and the second metal oxide may be oxides of different metals, wherein the first metal oxide and the second metal oxide are It can be used as an additive for Ti, Sn, Zn, Mn, Mg, Ni, W, Co, Fe, Ba, In, Zr, Cu, Al, Bi, Pb, Ag, Cd, Y, Mo, But is not limited thereto.

Further, by using oxides of metals different from each other as the first metal oxide contained in the core and the second metal oxide contained in the shell, a heterojunction is formed at the interface between the core and the shell of the core- a heterojunction can be formed.

The heterojunction may contribute to the improvement of the sensitivity of the sensor including the core-shell nanostructure. For example, the first metal oxide and the second metal oxide may have energy band structures different from each other Which in turn can form a depletion layer in the core-shell nanowire.

The depletion layer means a space in which a charge carrier is deficient. For example, in the case of a p-type semiconductor, a depletion layer may be a space in which a hole serving as a charge carrier is deficient. But the present invention is not limited thereto.

The thickness of the shell of the core-shell nanowire may be 1.1 to 2.9 times the Debye length, more preferably 1.5 to 2.5 times, and more preferably 1.9 to 2.1 times, but is not limited thereto. It is not.

The Debye length means a distance at which free electrons, which are negative particles given in the plasma, are shielded by the surrounding positive particles and can move by their own kinetic energy regardless of the outside, For example, when oxygen is adsorbed on the surface of an n-type shell, electrons, which are charge carriers of the n-type semiconductor, are transferred to oxygen, The term "device length" can be used to refer to the minimum distance at which electrons can move due to oxygen adsorption, as described above.

For example, the device length of any shell material is dependent on the inherent properties of the shell material, such as the dielectric constant, and the height of the potential barrier generated by the band bending phenomenon resulting from the heterojunction with the core material Can vary.

In general, the thickness of the surface depletion layer is known to be equal to the Debye length (Debye, _D ). However, the thickness of the depletion layer in the core-shell structure may be a value corresponding to the sum of the shell length of the shell and the shell length due to the interface between the core and the shell.

For example, in the core-shell nanowire according to the present invention, the core is indium oxide (In ₂ O ₃ ), the shell is zinc oxide (ZnO), and indium oxide-oxide The thickness of the depletion layer of the zinc nanowire is determined by the sum of _D (ZnO), which is the thickness of the zinc oxide, which is the thickness of the depletion layer on the surface of the zinc oxide, and the sum of the divider lengths generated in the zinc oxide by the indium oxide and zinc oxide interfaces ( _D (In ₂ o ₃ ) + _D (ZnO)).

If the thickness of the zinc oxide is greater than twice the thickness of _D (ZnO), when the nanowire is exposed to air, the oxygen particles extract electrons from the conduction band of zinc oxide and a depletion layer of _D (ZnO) _A depletion layer of _D (ZnO) will be generated, but a channel through which electrons pass may be formed between the two.

However, if the thickness of the zinc oxide is coated to less than twice the length of _D (ZnO), the depletion layer between the depletion layer and the interface of the nanowire surface will be in contact with each other, And exhibits a higher resistance value. On the other hand, when the nanowire of the core shell structure reacts with a reducing gas such as ethanol, the electrons are supplied to the conduction band of the shell layer to lower the resistance.

Therefore, as the thickness of the shell layer is increased, the amount of electrons supplied to the conduction band of the shell layer during the supply of the reducing gas also increases, and the resistance can be reduced. If the thickness of the shell layer becomes equal to 2 _D (ZnO) , The shell layer will be supplied with the largest amount of electrons.

In other words, the nanowire having the maximum resistance upon exposure to air will receive the maximum electrons upon contact with the reducing gas, and as a result will exhibit maximum gas detection responsiveness. On the other hand, if the thickness of the shell layer is thicker than 2 _D (ZnO), the amount of electrons to be supplied due to contact with the reducing gas will be limited only to the thickness of _D (ZnO) . Therefore, the gas detection capability using this will also decrease.

Therefore, the thickness of the shell of the core-shell nanowires according to the present invention is preferably 1.1 to 2.9 times, more preferably 1.5 to 2.5 times, more preferably 1.9 to 2.1 times the length of the shell material divisor.

Further, the core-sensor including a shell nanowire is hydrogen (H _2), carbon monoxide (CO), methane (CH _4), ammonia (NH _3), methanol (CH ₃ OH), ethanol (C ₂ H ₅ OH ), Propane (C ₃ H ₈ ), hydrogen sulfide (H ₂ S), benzene, dimethylamine, triethylamine, toluene and xylene But is not limited thereto.

Further, according to the present invention,

Forming a core comprising a first metal oxide on a substrate (step 1);

Forming a sensing portion including the core-shell nanowire by forming a shell including a second metal oxide on the core (Step 2); And

And forming an electrode layer on the sensing unit (step 3)

Wherein the thickness of the shell is 1.1 to 2.9 times the length of the device.

Hereinafter, a method of manufacturing a sensor including the core-shell nanowire according to the present invention will be described step by step.

Step 1 is a step of forming a core comprising a first metal oxide on the substrate, it is possible to use a metal oxide semiconductor, TiO _2, SnO _2, ZnO, MnO _2, MgO, NiO, WO _3, Co ₃ O ₄ , Fe ₂ O ₃ , BaTiO ₃ , In ₂ O ₃ , ZrO ₂ , CuAlO _2, and Bi ₂ O _3, or a metal oxide complex, may be used to form nanowires through thermal vapor deposition and sputtering. But is not limited thereto.

Next, step 2 is a step of forming a sensing part including core-shell nanowires by forming a shell containing a second metal oxide on the core, wherein the shell of step 2 is formed by atomic layer deposition Layer Deposition (ALD).

The thickness of the shell can be controlled by adjusting the number of cycles (number of cycles) of the atomic layer deposition method. At this time, the thickness of the shell may be 1.5 to 2.5 times or 1.9 to 2.1 times the device length of the metal oxide.

Next, an electrode layer is formed on the sensing portion. The electrode layer may be a single-layer electrode layer containing a metal such as Au, Pt, or Cu, or a multi-layered electrode layer containing a metal such as Ti, Ni, or Cr in addition to the electrode layer of the single layer.

Among the metals included in the electrode layer, Au, Pt, or Cu may function substantially as an electrode. For example, Ti, Ni, or Cr among the metals included in the electrode layer may be a metal But it is not limited thereto.

The electrode layer may be formed by a method commonly used for forming electrodes such as a sputtering method or an evaporation method, but is not limited thereto.

The gas detection characteristic using the core-shell structure nanowires manufactured through the above manufacturing method can be explained by a combination of the carrier movement model by the potential barrier control and the surface depletion model. By adjusting these conditions, the sensor can be fabricated to maximize the gas detection characteristics by combining the optimum elements. In particular, the thickness of the optimal shell layer can be determined and the principle can be explained.

For example, in a nanowire including an indium oxide core and a zinc oxide shell, when the indium oxide nanowire is exposed to air, electrons present on the conduction band of indium oxide are attracted to oxygen atoms on the surface by oxygen atoms do. Thus, oxygen particles change into ionic forms such as O ^- , O ^{2 -} , and O ₂ ^- , which are ionic chemical species.

Also, as the oxygen ions on the surface increase, the potential barriers of the nanowires also increase, resulting in increased resistance. However, when the ethanol gas is supplied to the surface of the nanowire thereafter, this gas can act as a reducing agent.

Ethanol gas reacts with oxygen on the surface of the nanowire to form CO ₂ Or H ₂ O. In this process, electrons are generated and supplied to the nanowires. The depletion layer formed on the surface of the nanowire by the electrons decreases, and the resistance decreases again. The process of supplying electrons to the nanowire surface by supplying ethanol gas is as follows.

C ₂ H ₅ OH (gas) → C ₂ H ₅ OH (ads) (1)

C ₂ H ₅ OH (ads) + 6O ^- (ads) 2CO ₂ (gas) + 3H ₂ O (gas) + 6e ^- (2)

The result is to increase the carrier concentration in the nanowire, thereby reducing the thickness of the depletion layer. In other words, the depleted electrons are returned to the conduction band to reduce the resistance of the nanowires constituting the sensor. The oxygen adsorption characteristics and the very high volume-to-surface area ratio of the indium oxide nanowire act as a property for greatly enhancing the gas detection characteristic.

Figs. 6 (a) and 6 (b) are schematic diagrams showing energy band diagrams in a state of post-equilibrium bonding between the zinc oxide and the indium oxide. The electron affinities of indium oxide and zinc oxide are known to be 3.5 eV and 4.35 eV, respectively. In the case of indium oxide and zinc oxide, the energy band gaps are 3.6 eV and 3.37 eV, respectively. Debye lengths of indium oxide and zinc oxide are 25 nm and 21.7 nm, respectively.

In the case of indium oxide and zinc oxide, the exact Fermi level is not known, but it is estimated that indium oxide is somewhat higher than zinc oxide as an approximate value. Each undoped material exhibits n-type semiconductor properties in both zinc oxide and indium oxide. If indium oxide and zinc oxide, both semiconductor materials of n type, form a heterojunction, the electrons will flow from the indium oxide towards the zinc oxide, and this phenomenon will occur until the Fermi levels of the two materials are equal .

Since the two materials form a hetero-junction, there is an interface between the two materials and an energy barrier will occur around the interface between the two materials. There are very dense defects in the vicinity, which results in high surface energy. Thus, energy increases similar to those on the surface of the material appear in the vicinity, which is caused by lattice mismatch between indium oxide and zinc oxide. Another phenomenon is the phenomenon of electron restraint that occurs when two substances are bonded together. This phenomenon is caused by the surface level of the interface between the two materials near both the bonding surfaces of indium oxide and zinc oxide.

As described above, the following two phenomena appear between the interface between indium oxide and zinc oxide: a phenomenon in which electrons move between interfaces due to a difference in Fermi energy level between indium oxide and zinc oxide, It is a phenomenon of electron restraint by surface level. The constraint of such a carrier serves as a factor for forming a depletion layer in both the indium oxide and zinc oxide regions with the intervening interface therebetween. Thus, a substantial energy band diagram of the equilibrium indium oxide and zinc oxide junctions appears similar to that at the interface of the polycrystalline silicon, as shown in FIG. 6 (c).

Therefore, in the core shell structure, the factors that change the resistance can be explained by the following three factors. First, there is a depletion layer generated by a combination of a depletion layer at the surface of the core shell structure and a depletion layer at the interface between the heterojunctions. In addition, it is a phenomenon of controlling the movement of carriers caused by the potential barrier generated in the heterojunction and controlling the movement of carriers due to the potential barrier generated between the nanowires.

In the present invention, the efficiency of the ethanol detection sensor is maximized based on three factors that change the resistance, and the present invention will be described in detail with reference to the following examples. However, the following examples are illustrative of the present invention, and the present invention is not limited by the following examples.

& Lt; Example 1 > Preparation of indium oxide / zinc oxide nanowire

Step 1: Indium oxide nanowires were synthesized by thermal vapor deposition using indium powder using a Si substrate coated with gold.

Specifically, in order to synthesize indium oxide nanowire, a 3 nm gold coated c-axis grown sapphire wafer was used as a substrate. This substrate was used as a support for growing indium oxide nanowires. In order to coat 3 nm of gold on the substrate, a dc sputter target was used. Then 99.99% pure indium powder was placed in an alumina crucible and the gold-coated side was placed on the crucible containing the powder. The distance between the indium powder and the sapphire substrate was about 5 mm. The crucible was charged into the center of the horizontal quartz tubular furnace, and a vacuum was maintained. At this time, the vacuum was set to 1 mTorr. The temperature of the furnace was raised to 800 DEG C while maintaining a vacuum at a heating rate of 10 DEG C per minute.

Then, when the set temperature was reached, 100 sccm of nitrogen was flowed and 0.1 sccm of oxygen was allowed to flow to allow oxygen to flow at a concentration of 0.1%. At this time, oxygen serves to oxidize indium to become indium oxide, and nitrogen acts as a carrier gas. In order to suppress the abrupt reaction, the oxygen concentration was controlled to 0.1 1%. The pressure for this reaction was limited to 0.5 Torr and 5 Torr.

After maintaining this state for 1 hour, the supply of gas was stopped and a vacuum of 1 mTorr was again made, and the furnace was cooled to room temperature. During the cooling, it was cooled down for about 2 hours. At room temperature, the vacuum was removed from the tubular furnace, and the specimen was taken out. It can be seen that the gold coating of the specimen is coated with a cloudy thin film with bright yellow light.

Step 2: Based on the thin film-coated substrate prepared in step 1, zinc oxide was coated using atomic layer deposition (ALD) method.

Specifically, diethylzinc (DEZn) was used as a precursor of zinc and DI Water was used as a raw material of oxygen. For coating using atomic layer deposition, two materials were separated and injected sequentially. During the injection of the two materials, nitrogen purge was performed in the middle to prevent the two materials from being mixed in the chamber.

First, the vacuum of the chamber was set to 1 mTorr, the temperature was raised to 150 캜, and then dimethylzinc was injected for 0.15 seconds. Then, nitrogen was purged for 3 seconds, DI water was injected for 0.2 second, and nitrogen purge was performed for 3 seconds. During the above operation, the pressure in the chamber was maintained at 0.1 Torr, and eleven specimens were fabricated from 0 to 100 cycles, each of which was increased by 10 cycles in order to synthesize various thicknesses.

Step 3: The thickness of zinc oxide shell coated on each cycle was examined through a low magnification transmission electron microscope photograph of nanowires coated with each cycle manufactured in step 2 above. The thickness of the shell of the specimen was extracted from the thickness of the specimen. The thickness of 0, 30, 40, 50, 60, 70, and 80 cycles of 0 nm, 17 nm, 27 nm, 34 nm, Zinc oxide coated nanowires were prepared.

Example 2: Manufacture of a sensor including indium oxide / zinc oxide nanowire

An IDE (Interdigital Electrode) pattern chip was fabricated to fabricate a gas detection sensor including the indium oxide / zinc oxide nanowire fabricated in Example 1.

In order to fabricate chips, IDE patterns were formed by photolithography on a 1 cm ² SiO ₂ / Si (200 nm oxide) substrate. At this time, the line width of the pattern was set to 20 탆. As the electrode material of the pattern, Ni of 200 nm and Au of 50 nm were coated as an adhesive layer and an electrode layer, respectively.

The nanowires prepared in Example 1 were dispersed in the IDE pattern to form a channel. The nanowire-synthesized substrate was placed in a mixed solution of 5 ml of IPA (Iso Propyl Alcohol) and 5 ml of DI Water, followed by ultrasonic agitation for 30 seconds. Then, 1 ml of the nanowire-agitated suspension was dropped on an IDE chip and then dried. After that, the nanowires were connected to each other to form a channel between the IDE patterns, and a sensor including indium oxide / zinc oxide nanowires was completed.

≪ Comparative Example 1 &

Only the step 1 in Example 1 was carried out to synthesize indium oxide nanowires.

≪ Comparative Example 2 &

A sensor including indium oxide was completed in the same manner as in Example 2, except that the indium oxide nanowire produced in Comparative Example 1 was used.

EXPERIMENTAL EXAMPLE 1 Analysis of physical properties of indium oxide / zinc oxide nanowire

In order to observe the shape of the indium oxide / zinc oxide nanowire fabricated in Example 1, it was analyzed by a scanning electron microscope, and it is shown in FIG. As shown in FIG. 1, the indium oxide / zinc oxide nanowire has a diameter of about 150 nm and a length of 10 to 30 μm.

In addition, there is a limitation that only the apparent shape of the nanowire can be grasped and analyzed through a transmission electron microscope, which is shown in FIG.

FIG. 2 (a) shows a low-magnification transmission electron microscope photograph showing nanowire patterns of a core-shell structure. FIG. 2 (b) shows a high magnification transmission electron microscope photograph showing that the indium oxide layer and the zinc oxide layer are clearly distinguished from each other, and a different lattice pattern appears from the interface between the two layers, The zinc layer was polycrystalline and the indium oxide layer was single crystal. In the case of the lattice pattern, the indium oxide layer showed an interstitial distance of 0.413 nm and 0.292 nm, which represents the indium oxide plane of (211) and (222). On the other hand, it can be confirmed that the zinc oxide layer exhibits a (101) plane of 0.248 nm.

Then, in order to check the shape of the nanowire crystals, SAED (Selected Area Electron Diffraction) analysis was performed and this is shown in FIG. 2 (c). As shown in Fig. 2 (c), well-aligned dots and ring-shaped lines appear, each point representing indium oxide and the ring representing zinc oxide. In case of zinc oxide, it was formed as polycrystalline and showed ring shape result.

Also, an X-ray diffraction analysis was performed to confirm the crystal change of the indium oxide / zinc oxide nanowire before and after the zinc oxide coating of the material, and the XRD pattern of the nanowire is shown in FIG. Most of the XRD pattern peaks shown in the graph of Fig. A peak showing a BCC indium oxide 89-4595 (In ₂ O _3). Also, a zinc oxide (ZnO) peak of JCPDS No. 89-1397 appeared, which can be judged to be due to the structure of indium oxide as a core and zinc oxide as a shell.

≪ Experimental Example 2 >

In order to investigate the ethanol gas detection characteristics using the sensor manufactured according to the present invention, the zinc oxide / nano wire having the thicknesses of 0 nm, 17 nm, 27 nm, 34 nm, 44 nm and 53 nm Were investigated for the reactivity of ethanol gas at 1000 ppm. The temperature of the experiment was raised to 300 ° C., the humidity was controlled to 50% RH, and the ethanol gas supplied for the detection reaction characteristics was maintained at 1000 ppm and 200 sccm. At rest, 200 sccm of air was injected.

The results of the analysis are shown in FIG. 4, and FIGS. 4 (a) and 4 (b) are graphs showing changes in the detection reaction characteristics depending on the thickness of the shell of the indium oxide / zinc oxide nanowire.

According to the graph of FIG. 4, it can be seen that the ability of the indium oxide to detect ethanol gas is highly sensitive to the thickness of the zinc oxide coated on the surface of the nanowire. It can be assumed that the size of the depletion layer formed in the zinc oxide layer changes depending on the thickness of the coating layer.

Also, the coating layer exhibiting the highest reactivity in the above experiment was found to be about 44 nm in thickness, and this thickness corresponds to a length nearly twice the Debye length of zinc oxide. The Debye length ( _D ) of zinc oxide is about 21.7 nm, so 43.4 nm, twice this length, can be about the same thickness, which is different from the coated thickness of 44 nm and 0.6 nm. The results strongly indicate that the thickness of the shell exhibiting the highest reactivity in the core shell structure appears at twice the Debye length. In other words, it can be seen that the depletion layer of the surface is maximized at a thickness twice as large as the Debye length when the gas is supplied from the core-shell nanowire.

Based on the results of the above analysis, it was found that the optimum detection reaction occurs at a thickness of 44 nm, and the sensor including the simple synthesized indium oxide nanowire prepared in Comparative Example 2 and the 44 The gas detection reaction characteristics of various concentrations of ethanol gas were analyzed using a sensor including indium oxide / zinc oxide nanowire coated with zinc oxide nanometer thick, which is shown in FIG. 5 and Table 1.

FIG. 5 (a) is a graph showing the ethanol detection reaction characteristics of a sensor including a simple synthesized indium oxide nanowire and FIG. 5 (b) showing an indium oxide / zinc oxide nanowire.

In order to perform the detection reaction experiment, the temperature of the chamber was maintained at 300 ° C. and the concentration of ethanol gas supplied for the detection reaction was 200, 400, 600, 800 and 1000 ppm. The resistance was decreased when the ethanol gas was supplied, and when the air gas was flown afterwards, the resistance returned to the original state and returned to the original state. Even if the detection reaction was repeated, the resistance recovered to the initial state at the time of recovery, and the hysteresis phenomenon was not exhibited.

Response, R _a / R _g (%) Ethanol concentration (ppm) Comparative Example 2
(Simple oxide indium nanowire) Example 2
(Indium oxide / zinc oxide nanowire) 200 7.47 ± 2.0 18.80 ± 2.0 400 13.15 ± 2.0 36.73 ± 2.0 600 17.52 ± 2.0 58.77 ± 2.0 800 22.10 ± 2.0 106.38 ± 2.0 1000 29.98 ± 2.0 196.15 ± 2.0

As shown in Table 1, defined by calculating the expression (R _a / R _g) was a * 100% In order to confirm the reactivity of the gas is detected, this time, R _a is the resistance, R _g when the supply air is experimental gas Is shown in Fig.

As shown in FIG. 5 and Table 1, Comparative Example 2, which is a sensor including a simple synthesized indium oxide nanowire, showed a change of about 750 to 3000% as the concentration of ethanol gas changed from 200 ppm to 1000 ppm . On the other hand, the sensor including the nanowire of the indium oxide / zinc oxide shell of Example 2 showed a change of 1,880 to 19620%. From the above results, it can be confirmed that the ethanol gas detection ability of the nanowire is about 6 times or more based on the presence of the zinc oxide layer at 1000 ppm.

In addition, the indium oxide / zinc oxide nanowire produced according to the present invention exhibits a detection characteristic that is higher than the limit of the ethanol detection characteristic of conventional simple synthesized indium oxide nanowire or zinc oxide nanowire, The optimal thickness for determining the thickness of the shell in the fabrication of the shell structure was found. Further, it is possible to manufacture a gas detection sensor with a further enhanced function by finding that the optimum thickness is substantially thicker than the optimum thickness claimed in the existing theory.

Furthermore, in the study of other gases and other gases other than ethanol gas detection using indium oxide core and zinc oxide shell, it is expected that a further increased gas detection sensor can be produced by using a new shell thickness.

Claims (10)

materials;
A core-shell nanowire comprising a core comprising indium oxide (In ₂ O ₃ ) formed on the substrate and a shell comprising zinc oxide (ZnO); And
And an electrode layer on the core-shell nanowire,
Wherein the thickness of the shell of the nanowire is 1.1 to 2.9 times the Debye length.
delete 2. The sensor of claim 1, wherein the thickness of the shell has a value of 1.5 to 2.5 times the shell device length.
2. The sensor of claim 1, wherein the thickness of the shell has a value of 1.9 to 2.1 times the shell device length.
The method of claim 1, wherein the sensor comprising the core-shell nanowire comprises at least one of hydrogen (H _{2 )} , carbon monoxide (CO), methane (CH ₄ ), ammonia (NH ₃ ), methanol (CH ₃ OH) ₂ H ₅ OH), propane (C ₃ H ₈ ), hydrogen sulfide (H ₂ S), benzene, dimethylamine, triethylamine, toluene and xylene Wherein the sensor detects at least one gas selected from the group consisting of the core-shell nanowires.
delete Forming a core containing indium oxide (In ₂ O ₃ ) on the substrate (step 1);
Forming a sensing portion including the core-shell nanowire by forming a shell containing zinc oxide (ZnO) on the core (Step 2); And
And forming an electrode layer on the sensing unit (step 3)
Wherein the thickness of the shell is 1.1 to 2.9 times the shell device length.
8. The method of claim 7, wherein the shell of step 2 is formed through atomic layer deposition.
8. The method of claim 7, wherein the thickness of the shell is controlled through the number of cycles (number of cycles) of atomic layer deposition.
8. The method of claim 7, wherein the thickness of the shell is 1.5 to 2.5 times the shell length.

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