KR102296352B1 - Metal oxide nanowire arrays, and method for preparing the same - Google Patents

Abstract

The present invention relates to a metal oxide nanowire array and a method for manufacturing the same, wherein the metal oxide nanowire array comprises a nanofiber film in which nanofibers aligned in one direction are integrated, and a metal oxide coating layer coated on the nanofiber film. include
The metal oxide nanowire array can be applied as an optical sensor by exhibiting improved photocurrent characteristics under UV irradiation conditions, and the efficiency, resolution, and sensitivity of the optical sensor can be improved.

Description

METAL OXIDE NANOWIRE ARRAYS, AND METHOD FOR PREPARING THE SAME

The present invention relates to a metal oxide nanowire array and a method for manufacturing the same, and more particularly, to a metal that exhibits improved photocurrent characteristics under UV irradiation conditions and can be applied as an optical sensor, and can improve the efficiency, resolution and sensitivity of the optical sensor It relates to an oxide nanowire array and a method for manufacturing the same.

Metal oxides such as zinc oxide (ZnO) are versatile semiconductor materials used in a wide range of applications in electronics, photonics and optics. In particular, bulk ZnO is a broadband gap (3.37 eV) semiconductor that generates electrons at electromagnetic wavelengths shorter than the ultraviolet (UV) range. A sensor with a ZnO layer deposited under UV irradiation conditions can detect a change in resistance and detect a gaseous chemical through a reduction oxidation reaction.

Recent research has focused on improving the sensor's performance parameters including sensitivity, selectivity, stability, resolution, linearity and efficiency. Nanostructures with high specific surface area exhibit excellent mechanical strength, chemical sensitivity, and improved electrical and optical properties. For example, nanoscale structures with nanoparticles, nanowires, nanobelts, nanorings and nanoflakes are used to improve the surface response of optical sensors. Among these, metal oxide nanowires (ZnO NWs) exhibit improved electrical properties compared to metal oxide thin films due to the electrical resistance of chemicals under UV irradiation.

In order to utilize the advantages of nanostructured films in commercial sensors, they must be mass-produced with a simple manufacturing process. The process for mass production of metal oxide nanowires at low cost should be performed under atmospheric conditions. In addition, the synthesis process of metal oxide nanowires should not damage the structure of the polymer substrate during mass production to obtain a low defect rate sensor device.

Hydrothermal synthesis is a method of crystallizing nanoparticles from an ionized aqueous solution under atmospheric pressure conditions. Using this, a metal oxide nanowire-based sensor can be manufactured using a polymer nanofiber film obtained using electrospinning.

However, in the production of nanofiber films through the conventional electrospinning technique, the film is laminated on the surface of a plate-type or drum-type metal collector and is affected by an electric field formed around the metal collector. Since there is no potential difference when the plate-type or drum-type metal collector has the same height away from the surface of the collector, a nanofiber film having a Gaussian-shaped thickness distribution is formed.

In particular, uniformity is important in the manufacturing process of a nanofiber film for use as a sensor substrate or filter. However, it is difficult for a nanofiber film formed on a collector with no potential difference to have a uniform thickness distribution, and damage to the film easily occurs in the process of transferring the film formed on the surface of the collector to another film. This causes a decrease in productivity and an increase in cost, and a technology is required to solve the problem.

It is an object of the present invention to provide a metal oxide nanowire array that can be applied as an optical sensor by exhibiting improved photocurrent characteristics under UV irradiation conditions, and can improve the efficiency, resolution and sensitivity of the optical sensor.

Another object of the present invention is to provide a method for manufacturing the metal oxide nanowire array.

According to an embodiment of the present invention, there is provided a metal oxide nanowire array including a nanofiber film in which nanofibers aligned in one direction are integrated, and a metal oxide coating layer coated on the nanofiber film.

The nanofibers may be made of poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE).

In the nanofiber film, 80% (number) to 100% (number) of the nanofibers may be aligned at an orientation angle of -45 degrees to +45 degrees with respect to the average orientation angle of the nanofibers.

The nanofiber film may have a thickness of 10 μm to 100 μm.

The nanofiber film may be a laminated nanofiber film in which 1 to 5 nanofiber films are laminated.

According to another embodiment of the present invention, by electrospinning a polymer solution between a pair of wire electrode collectors disposed to face each other at an interval, a nanofiber film formed by integrating nanofibers aligned in one direction It provides a method of manufacturing a metal oxide nanowire array comprising the step of manufacturing, and forming a metal oxide coating layer through hydrothermal synthesis on the nanofiber film.

The pair of metal wires may have a diameter of 0.5 mm to 5 mm.

The pair of metal wires may have a length of 100 mm to 300 mm.

A distance between the pair of metal wires may be 30 mm to 100 mm.

During the electrospinning, the supply flow rate of the polymer solution may be 0.1 μl/s to 0.3 μl/s.

During the electrospinning, a distance between the nozzle tip and the electrode collector may be 70 mm to 150 mm.

During the electrospinning, the voltage may be 8 kV to 20 kV.

In the electrospinning, the time may be 5 to 20 minutes.

The method of manufacturing the metal oxide nanowire array may further include transferring the prepared nanofiber film onto a substrate, and forming the metal oxide coating layer may be made on the nanofiber film supported on the substrate. have.

The manufacturing method of the metal oxide nanowire array further comprises the step of manufacturing a laminated nanofiber film by laminating a plurality of the nanofiber films, and the metal oxide coating layer may be formed on the laminated nanofiber film.

The step of forming the metal oxide coating layer, forming a metal oxide nanoparticle seed (seed) on the nanofiber film, and immersing the nanofiber film in a solution containing a metal oxide precursor, 80 ℃ to 120 It may include the step of growing the metal oxide by low-temperature hydrothermal synthesis at a temperature of ℃ for 6 hours to 12 hours.

The metal oxide nanowire array of the present invention exhibits improved photocurrent characteristics under UV irradiation conditions, so it can be applied as an optical sensor, and the efficiency, resolution and sensitivity of the optical sensor can be improved.

In the method for manufacturing a metal oxide nanowire array of the present invention, there is no damage in the desorption process after film production, and it is possible to form an electrospun film having a uniform thickness distribution through electric field control. By controlling the directionality and manufacturing time, the photosensitive performance of the electrospun nanofiber-based metal oxide nanowire array can be improved, and high-efficiency, flexible optical sensors can be mass-produced at low cost.

1 is a diagram schematically illustrating a method of manufacturing a metal oxide nanowire array.
2 and 3 are SEM images of ZnO NWs (nanowires) formed on a randomly oriented ES NF (electrospun nanofiber) film and ZnO NWs formed on an aligned ES NF film, respectively.
4 is an SEM image and an angle distribution histogram of ZnO NWs formed on an aligned ES NF film.
5 is an XRD measurement result of ZnO NWs formed on a randomly oriented ES NF film and ZnO NWs formed on an aligned ES NF film.
6 is a current-voltage curve (IV characteristics) of ZnO NWs formed on a randomly oriented ES NF film and ZnO NWs formed on an aligned ES NF film.
FIG. 7 is It characteristics of ZnO NWs formed on a randomly oriented ES NF film and ZnO NWs formed on an aligned ES NF film.
8 is a graph showing the change in resistance of the ZnO NW according to the manufacturing time of the ES NF film.

Hereinafter, the present invention will be described in more detail.

The metal oxide nanowire array according to an embodiment of the present invention includes a nanofiber film in which nanofibers aligned in one direction are integrated, and a metal oxide coating layer coated on the nanofiber film.

The nanofibers constituting the nanofiber film may be made of a polymer having a melting point of 95 °C or higher. The polymer is polyacrylic acid (PAA), polystyrene sulfonic acid (PSSA), polymethyl methacrylate (PMMA), polymethyl acrylate (PMA), polyvinyl acetate (polyvinyl acetate, PVAc), polyvinyl pyrrolidone (PVP), polyvinyl alcohol (polymethyl alcohol, PVA), polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polyethylene oxide ( polyethylene oxide, PEO), polypropylene oxide (PPO), polystyrene (PS), polytrifluoroethylene (PTFE), copolymers thereof, and mixtures thereof may be any one selected from the group consisting of and specifically poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE).

Poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE) has excellent chemical resistance and a high melting point of 171 °C, and is suitable for hydrothermal synthesis to form metal oxide nanowires. In addition, unlike other fluorine-based resins, it has excellent mechanical properties, so there is no difficulty in manufacturing it in various sizes.

In this case, the nanofiber film may be formed by integrating nanofibers aligned in one direction. Here, the meaning that the nanofibers are aligned in one direction means that the nanofibers are generally oriented in one direction, which is opposite to the random orientation in which the nanofibers are randomly oriented. Specifically, 80% (number) to 100% (number) of the nanofibers may be aligned at an orientation angle of -45 degrees to +45 degrees with respect to the average orientation angle of the nanofibers, specifically -20 degrees to +20 degrees It may be aligned at an orientation angle, and more specifically, it may be aligned at an orientation angle of -10 degrees to +10 degrees.

Here, the percentage (number) of nanofibers is a percentage of the number of nanofibers having an orientation angle of a certain range with respect to the total number of nanofibers constituting the nanofiber film. The orientation angle of the nanofiber means an acute angle (small angle) formed by each nanofiber with respect to any one direction of the nanofiber film. Any one direction of the nanofiber film may be, for example, a width direction, a length direction, or a diagonal direction of the nanofiber film. The orientation angle of the nanofiber may be measured at the midpoint of the nanofiber. The average orientation angle of the nanofibers is a value obtained by dividing the sum of the orientation angles of each of the nanofibers by the number of nanofibers. At this time, the population of nanofibers for obtaining the average orientation angle is preferably all the nanofibers constituting the nanofiber film, but counting only the nanofibers within a certain range of the nanofiber film, or using only the nanofibers spaced apart from the entire nanofiber film It is also possible to calculate

When the orientation angle of the nanofibers is greater than +45 degrees to -45 degrees with respect to the average orientation angle of the nanofibers, the nanofibers do not span between the electrodes, and the shortest length of the nanofibers placed between the electrodes increases, resulting in a large resistance. have.

The thickness of the nanofiber film may be 10 μm to 100 μm, specifically 30 μm to 60 μm. In this case, the nanofiber film may be a laminated nanofiber film in which 1 to 5 nanofiber films are laminated to have such a thickness. If the thickness of the nanofiber film is less than 10 μm, the durability of the nanofiber film may be reduced, and if it exceeds 100 μm, the resistance of the sensor is 1 GΩ or more, so the precision of the sensor expressed in the resistance ratio may be reduced.

The metal oxide coating layer may be coated on the nanofiber film, and specifically, the metal oxide coating layer may be formed on the surface of each of the nanofibers constituting the nanofiber film. That is, the nanofibers of the nanofiber film may be coated with a metal oxide to become a metal oxide nanowire.

The metal oxide can be used without limitation as long as it is a broadband gap semiconductor that generates electrons at an electromagnetic wavelength shorter than the ultraviolet (UV) range, for example, ZnO, TiO ₂ , SnO ₂ , Ga ₂ O ₃ , In ₂ O ₃ , It may be any one selected from the group consisting of GaN, AlN, InN, SiC, and mixtures thereof. In particular, when zinc oxide (ZnO) is used, it is easy to form a nanowire structure through a hydrothermal synthesis process.

The metal oxide coating layer is grown along the surface of the nanofiber, has high crystallinity, and thus may have high intensity at the diffraction peaks of (100), (002) and (101).

The metal oxide nanowire may have a length of 5 μm to 11 μm, specifically 5 μm to 6 μm. Since the surface area is reduced as the length of the metal oxide nanowire is shorter, the efficiency may be lowered in sensor application.

The metal oxide nanowire may have a diameter of 30 nm to 200 nm, specifically 30 nm to 60 nm. As the diameter of the metal oxide nanowire decreases, the size of the nanowire decreases, which leads to a decrease in surface area. In addition, as the length of the nanowire is shorter, the number of electrons that are excited under the light irradiation condition may be reduced. In addition, since the exposed area should be wide, it is advantageous that the aspect ratio of the nanowire is large.

The metal oxide nanowire array exhibits improved photocurrent characteristics under UV irradiation conditions, so it can be applied as an optical sensor, and the efficiency, resolution, and sensitivity of the optical sensor can be improved. Accordingly, metal oxide nanowires can be applied to various fields such as optical sensors, functional filters, drug delivery layers, battery separators, and cell culture scaffolds.

In a method of manufacturing a metal oxide nanowire array according to another embodiment of the present invention, a polymer solution is electrospinning between a pair of wire electrode collectors disposed to face each other at a distance, and the nano-aligned nanowires are aligned in one direction. Manufacturing a nanofiber film in which fibers are integrated, and forming a metal oxide coating layer on the nanofiber film through hydrothermal synthesis.

1 is a diagram schematically illustrating a method of manufacturing a metal oxide nanowire array. Hereinafter, a method of manufacturing a metal oxide nanowire array will be described with reference to FIG. 1 .

First, the polymer solution 12 is electrospun to prepare the nanofiber film 20 (S10).

The polymer solution 12 may be prepared by dissolving a polymer for forming nanofibers in an organic solvent. Since the description of the polymer for forming nanofibers is the same as that of the metal oxide nanowire array, a repetitive description will be omitted. The organic solvent is dimethylacetamide (N,N-dimethylacetamide), dimethylformamide (N,N-dimethyl formamide), dimethylsulphoxide, methylpyrrolidone (N-methyl-2-pyrolidone), triethylphosphate (triethylphosphate), methylethylketone (methylethylketone), tetrahydrofuran (tetrahydrofuran), acetone (acetone), and may be any one selected from the group consisting of mixtures thereof.

Electrospinning can be made using a pair of wire electrode collectors 11, and through this, it is possible to manufacture a highly aligned nanofiber film 20 in a free support state. A pair of wire electrode collectors 11 are disposed on the same plane facing each other at a distance, and a polymer solution 12 is disposed on a nozzle positioned on the same plane in which the pair of wire electrode collectors 11 are positioned. is supplied At this time, the polymer solution is transported by forming a jet by the difference in electrical energy between the nozzle and the pair of wire electrode collectors 11 , that is, the voltage difference. The formed jet is whipped and stretched by an electric field to become thinner, and the solvent is vaporized so that the solid-state nanofibers are accumulated while being aligned in a predetermined direction between the pair of wire electrode collectors 11 .

The pair of metal wires may have a diameter of 0.5 mm to 5 mm, specifically 0.5 mm to 1 mm. When the diameter of a pair of metal wires is less than 0.5 mm, the metal wire may be deformed in the transfer step, and nanofibers may be formed only on the surface of the metal wire due to a high potential difference with the periphery, and if it exceeds 5 mm, the metal wire may be deformed. As the potential gradient formed around the wire gradually decreases, the alignment of the nanofibers may be lowered.

The pair of metal wires may have a length of 100 mm to 300 mm, and specifically 150 mm to 250 mm. If the length of the pair of metal wires is less than 100 mm, the uniformity of the thickness of the nanofiber film may be reduced.

The distance between the pair of metal wires may be 30 mm to 100 mm, specifically 40 mm to 60 mm. If the distance between the pair of metal wires is less than 30 mm, the thickness of the nanofiber film may be non-uniform, and if it exceeds 100 mm, the yield may be lowered, and fibers may be formed only on the surface of the metal wire.

The supply flow rate of the polymer solution 12 during electrospinning may be 0.1 μl/s to 0.3 μl/s, and specifically 0.15 μl/s to 0.17 μl/s. When the supply flow rate of the polymer solution 12 during electrospinning is less than 0.1 μl/s, the yield is low and production time may increase, and when it exceeds 0.3 μl/s, non-uniform droplets during the manufacturing process of the nanofiber film ) can be generated on the surface.

The distance between the nozzle tip and the electrode during electrospinning may be 70 mm to 150 mm, specifically, 90 mm to 100 mm. When the distance between the nozzle tip and the electrode during electrospinning is less than 70 mm, a non-uniform nanofiber film may be formed because the solvent is not sufficiently evaporated due to the short spinning distance. can be formed.

The voltage during electrospinning may be 8 kV to 20 kV, and specifically 10 kV to 15 kV. When the voltage during electrospinning is less than 8 kV, the electrostatic repulsive force in the polymer solution is smaller than the surface tension, so nanofibers are not formed and droplets of the polymer solution can be splashed. It can be formed only on the surface of the metal wire.

The electrospinning time may be 5 minutes to 20 minutes, specifically 10 minutes to 15 minutes. If the electrospinning time is less than 5 minutes, the thickness uniformity of the nanofiber film may be reduced, and if it exceeds 20 minutes, the yield of the nanofiber film may be reduced due to the decrease in the strength of the electric field by the nanofibers.

Next, the prepared highly aligned nanofiber film 20 in a free support state is transferred onto the surface of various types of substrates 21 (S20).

Compared to the conventional electrospinning process, the free-supporting nanofiber film 20 has no damage in the detachment process, so that physical damage to the fiber in the transfer process can be minimized.

The kind of the substrate 21 capable of supporting the nanofiber film 20 is not limited, for example, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyethersulfone, polyimide, glass, etc. may be used. .

Optionally, in order to manufacture the nanofiber film 20 of a desired thickness, a plurality of nanofiber films 20 may be laminated to prepare a laminated nanofiber film. For example, the laminated nanofiber film may be one in which one to five nanofiber films 20 are laminated.

Next, on the nanofiber film 20, a metal oxide coating layer is formed through hydrothermal synthesis (S30).

Specifically, the step of forming the metal oxide coating layer is a step of forming a metal oxide nanoparticle seed 31 on the nanofiber film 20, and after immersing the nanofiber film 20 in a solution containing a metal oxide precursor , may include the step of growing the metal oxide by hydrothermal synthesis at low temperature.

The step of forming the metal oxide nanoparticle seed 31 on the nanofiber film 20 is, for example, seeding the metal oxide nanoparticles dispersed in the bipolar solvent on the nanofiber film 20 using a spin coater. can do.

The bipolar solvent may be any one selected from the group consisting of ethanol, methanol, dimethylformamide (DMF), tetrahydrofuran (THF), and mixtures thereof.

After immersing the nanofiber film 20 including the metal oxide nanoparticle seed 31 in a solution containing a metal oxide precursor, low-temperature hydrothermal synthesis is performed to grow the metal oxide to form a metal oxide coating layer. For example, the metal oxide precursor may be zinc nitrate hydrate (Zn(NO ₃ ) ₂ .6H ₂ O).

Low-temperature hydrothermal synthesis may be performed at a temperature of 80 °C to 120 °C for 6 hours to 12 hours, and specifically, at a temperature of 80 °C to 85 °C for 6 hours to 7 hours. If the low-temperature hydrothermal synthesis temperature is less than 80 ℃, it may be difficult to form a nanowire structure, and if it exceeds 120 ℃, physical deformation may occur in the nanofiber film. If the low-temperature hydrothermal synthesis time is less than 6 hours, it may be difficult to form a nanowire structure, and if it exceeds 12 hours, the growth rate in the longitudinal direction may be reduced.

The metal oxide nanowire array manufacturing method uses two parallel wire electrode collectors in an electrospinning process to form a highly aligned nanofiber film in a free support state, and transfer the film in a free support state to prepare a multilayer film and laminate it A nanofiber film is prepared. Compared to the conventional electrospinning process, there is no damage in the desorption process after film production, and it is possible to form a nanofiber film having a uniform thickness distribution through electric field control.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

[Production Example]

(Preparation Example 1: Preparation of nanofiber film)

Before electrospinning, the polymer solution was prepared in a completely molten state to ensure a homogeneous solution. Poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE, (75/25 mol %), Piezotec) powder was mixed with N,N-dimethylformamide (DMF, 99.8 %, Sigma Aldrich) with acetone. (99.5 %, Samjeon) 3 : 13 wt% was dissolved in a solvent of 7 volume ratio. The PVDF-TrFE solution was treated with a hot plate stirrer at 45 °C for 72 h.

The electrospinning equipment included a voltage source, a syringe pump, a metal needle, a flat plate collector (SUS sheet, 300 mm x 300 mm) and a coupling wire electrode collector (copper wire, D = 1 mm).

The PVDF-TrFE solution was placed in a syringe and pumped at a flow rate of ^{0.167 μl·s −1 through a 25 G metal needle using a syringe pump.} Then, the distance between the high voltage applied metal needle tip (11.5 kV) and the grounded flat plate or coupling wire collector was 95 mm.

In the flat plate collector, electrospun nanofibers (ES NF) were randomly oriented and integrated, and transferred to a polyethylene terephthalate (PET) film with a size of 20 mm x 20 mm. The production time of the ES NF film was 900 seconds.

On the other hand, in the two wire electrode collector, highly aligned ES NF films were obtained. The distance between the parallel wires was 55 mm. It took 300 seconds to make the ES NF film. The prepared free-supporting, highly aligned nanofiber film was transferred to a PET film. The manufacturing process of the ES NF film was repeated 3 times. Each ES NF was laminated onto a preformed ES NF film.

(Preparation Example 2: Preparation of ZnO nanowires)

A hydrothermal synthesis method was used to grow ZnO nanowires (NWs) on ES NF films. ZnO NPs (nanoparticles) are

2 h at 60 °C in ethanol (99.5%, Sigma-Aldrich) containing 30 mM sodium hydroxide (NaOH, 99.99%, Sigma-Aldrich) and 10 mM zinc acetate (Zn(OAc) _{2 , 99.99%, Sigma-Aldrich)} synthesized

After synthesizing ZnO NPs, ZnO NPs dispersed in ethanol were homogeneously seeded onto randomly aligned ES NF films on a spin coater at 100 rpm, which was repeated 5 times. Simultaneously, 25 mM zinc nitrate hydrate (Zn(NO ₃ ) ₂ .H ₂ O, 98%, Sigma Aldrich), 1 mM polyethyleneimine (PEI, MW~800, Sigma Aldrich), and 25 mM hexamethylene in distilled water Tetramine (HMTA, 99.5%, Sigma-Aldrich) was added and preheated at 95° C. for 1 hour to prepare a ZnO precursor.

ES NF films seeded with ZnO NPs were immersed in the ZnO precursor solution at 80 °C for 6 h. Zn ²⁺ ions were synthesized on the surface of ZnO NPs on the substrate and grown into a wire structure with c-axis (002) orientation.

[Experimental example]

(Experimental Example 1: Characteristics of ZnO Nanowires)

Scanning electron microscope (SEM) images were measured by JSM-IT300 (Jeol Ltd). X-ray diffraction (XRD) results were analyzed with an Empyrean (PANalytical) diffractometer. Current voltage and current time characteristics of the films were measured with a Keithley 2400 source meter.

In electrospinning for the production of random and ordered ES NF films, the electrospinning process was controlled under the same conditions except for the geometry of the collector. However, aligned ES NFs were fabricated between two wire electrodes in an independent state through electric field control under electrostatic spinning conditions.

2 and 3 are SEM images of ZnO NWs formed on randomly oriented ES NF films and ZnO NWs formed on aligned ES NF films, respectively.

Fully covered ZnO NWs along the ES NF surface were vertically grown to a length of 0.5 μm. The diameter of ZnO NWs formed on the surface of randomly oriented ES NFs (29.2 ± 6.95 nm) was 49.4% lower than that grown on aligned ES NFs (57.7 ± 15.0 nm) regardless of the same hydrothermal synthesis conditions. In the hydrothermal synthesis process, ZnO NPs seeded on ES NFs with low fiber diameters grew into nanowires and became small-length wires.

4 is an SEM image and angle distribution histogram of ZnO NWs formed on an aligned ES NF film. As shown in Figure 4, electrospinning using parallel copper wire electrodes produces highly ordered NF films. In couple wire collector electrospinning, 59% of ES NFs showed alignment under 10 degree orientation. In the NF fabrication process, highly aligned ES NFs could be obtained by changing the shape of the electrode plate only from a flat plate to two parallel lines without requiring any additional processes or equipment.

5 is an XRD measurement result of ZnO NWs formed on a randomly oriented ES NF film and ZnO NWs formed on an aligned ES NF film. As shown in Fig. 5, the XRD results show the crystallinity of ES NFs with and without ZnO NWs. In PVDF-TrFE, the semi-crystalline structure and the β-phase of the molecular chain are composed of a TTTT (All-trans) structure with ferroelectric properties. Despite the heat through hydrothermal synthesis during growth of ZnO NWs on the NF surface, the intensity of the β-phase (110) and (200) reflection peaks of the aligned ES PVDF-TrFE NFs were maintained at 2θ = 19.4. The low temperature conditions of hydrothermal synthesis did not affect the crystal structure of the ordered PVDF-TrFE ES NF. In addition, high crystals in the diffraction peaks of (100), (002) and (101) indicate highly oriented ZnO NW structures prepared through hydrothermal synthesis. Therefore, the XRD results indicate that the ZnO NWs on the aligned ES PVDF-TrFE NF films were prepared without being affected by the crystal structures of both ES NFs and ZnO NWs.

(Experimental Example 2: Optoelectric properties of ZnO nanowires)

Under UV irradiation conditions, ZnO NWs of the ES NF film generate electrons according to Planck's Equation 1 as follows.

[Equation 1]

E = hc/λ

In Equation 1, 'Planck constant h' and 'speed of light c' are represented.

Electrons from the ZnO NW surface are transferred through the 'bandgap energy E' (E = 3.37 eV), where the 'wavelength λ' of the light must be less than 375.71 nm. Therefore, electrons generated from the surface of ZnO NWs are transferred with low potential along the ZnO NWs on the ES NF surface under UV irradiation (λ = 365 nm) condition. Under continuous UV irradiation on the ZnO NW surface, electrons in the valence band are excited into the conduction band when the electrons gain sufficient energy. Excited electrons on the ZnO NW surface along the ES NF support tend to flow into the low current density region as they have strong current properties. The electrical conductivity of ZnO NWs is increased when using aligned ES NFs when compared to those of random ES NFs with a large gradient of current density.

As shown in Fig. 6, the movement of photo-induced electrons is affected by the orientation of the ES NF film. Current–voltage curves (IV characteristics) were plotted against the sheet resistance of ZnO NWs on randomly oriented ES NFs and those of ZnO NWs on aligned ES NF films under dark conditions and ^{with UV light of 2.5 μWcm −2} intensity (λ = 365 nm). measured under conditions. IV characteristics were measured at DC bias sweep voltages between -10 V and 10 V in 0.01 V increments.

ZnO NWs on randomly oriented ES NFs and ZnO NWs on aligned ES NFs exhibited linear sheet resistance characteristics regardless of geometrical features, although there was a difference in sheet resistance. The linearity errors of ZnO NWs in aligned and randomly oriented ES NF films were less than ±0.58% and ±1.60%, respectively. Under UV irradiation conditions, the sheet resistance of the ZnO NWs on the aligned ES NF film (0.17 MΩ/□) was 9.88 times lower than that for the ZnO NWs on the randomly oriented ES NF film (1.68 MΩ/□).

_{The sheet resistance ratios (R sq,off} / R _sq,on ) of the ZnO NWs of the aligned ES NF films to the ZnO NWs of the randomly oriented ES NFs were 551.0 and 47.8 in the UV irradiation condition and in the dark condition, respectively. The sheet resistance ratio of ZnO NWs on aligned ES NF films was 11.5 times that of ZnO NWs on random ES NF films. The current on the aligned ES NF surface showed a higher flow rate than the current on any ES NF surface. It can be seen that the geometry of the ES NF film substrate under the same hydrothermal conditions is an important factor in improving the photodetection performance of ZnO NWs in the ES NF film.

7 shows current-time curves (It characteristics) of ZnO NWs in randomly oriented ES NFs and aligned ES NFs under UV light corresponding to ^{0.5 μWcm −2} at 0.1 V bias with on and off cycles every 5 seconds.

ZnO NWs in aligned ES NFs and ZnO NWs in randomly oriented ES NFs show a rapid increase in initial-state current fluctuations at 374 s and 337 s, respectively, to steady-state (average current values within 5% (I _avg ± 5%)). After an operating time of 1500 s, the average current value remained steady. After a steady state of current fluctuation, the average current of the ZnO NWs of the _{aligned ES NF (I avg = 0.204 μA) was avg} = 0.026 μA) in ZnO NWs.In addition, _{the current difference between the maximum and minimum points (I on} -I _off ) was 5.377 nA in the ZnO NWs of the aligned ES NFs, and in the ZnO NWs in the randomly oriented ES NFs. 1.351 nA.

The thickness of the ES NF film also affected the sheet resistance. As shown in Fig. 8, the sheet resistance ratio (R _sq,off / R _sq,on ) of ZnO NWs on randomly oriented ES NF films increased with increasing fabrication time of ES NF films. The sheet resistance ratios were 192, 1105, and 1480, respectively, at the production times of the ES film at 15 minutes, 30 minutes and 60 minutes. This is because the proportion of ZnO NWs directly exposed to UV light is reduced compared to the total amount of ZnO NWs produced. Therefore, as the thickness of the ES NF film increases, the photoinduced electrons are easily dissipated in the depth direction of the ES NF film through the ohmic contact between the ZnO NWs. Accordingly, the increased sheet resistance ratio increased the sensitivity to the photodetector as the ES film fabrication time increased.

Although the preferred embodiment of the present invention has been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also provided. is within the scope of the

S10: nanofiber film manufacturing step
S20: nanofiber film transfer step
S30: metal oxide coating layer forming step
11: wire electrode collector
12: polymer solution
20: nanofiber film
21: substrate
31: metal oxide nanoparticles seed

Claims (12)

A nanofiber film in which nanofibers are integrated, and
A metal oxide coating layer coated on the nanofiber film
including,
The nanofibers are aligned in a direction parallel to the plane of the nanofiber film,
In the nanofiber film, 80% (number) to 100% (number) of the nanofibers are aligned at an orientation angle of -45 degrees to +45 degrees with respect to the average orientation angle of the nanofibers,
The metal oxide is _{any one selected from the group consisting of ZnO, TiO 2} , SnO ₂ , Ga ₂ O ₃ , In ₂ O ₃ , GaN, AlN, InN, SiC, and mixtures thereof,
Metal Oxide Nanowire Array. The method of claim 1,
The nanofibers are a metal oxide nanowire array made of poly (vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE). delete The method of claim 1,
A metal oxide nanowire array having a thickness of 10 μm to 100 μm of the nanofiber film. The method of claim 1,
The nanofiber film is a laminated nanofiber film in which 1 to 5 nanofiber films are laminated,
80% (number) to 100% (number) of the nanofibers included in the laminated nanofiber film are laminated to be aligned at an orientation angle of -45 degrees to +45 degrees with respect to the average orientation angle of the nanofibers metal oxide nanowire array. Electrospinning a polymer solution between a pair of wire electrode collectors disposed to face each other at a distance to prepare a nanofiber film in which nanofibers are integrated; and
Forming a metal oxide coating layer through hydrothermal synthesis on the nanofiber film
including,
The nanofibers are aligned in a direction parallel to the plane of the nanofiber film,
The nanofiber film is a metal oxide nanowire array in which 80% (number) to 100% (number) of the nanofibers are aligned at an orientation angle of -45 degrees to +45 degrees with respect to the average orientation angle of the nanofibers. manufacturing method. 7. The method of claim 6,
The pair of wire electrode collectors have a diameter of 0.5 mm to 5 mm,
The length of the pair of wire electrode collectors is 100 mm to 300 mm,
The distance between the pair of wire electrode collectors is a method of manufacturing a metal oxide nanowire array of 30 mm to 100 mm. 7. The method of claim 6,
During the electrospinning,
The feed flow rate of the polymer solution is 0.1 μl / s to 0.3 μl / s,
the distance between the nozzle tip and the electrode collector is 70 mm to 150 mm,
the voltage is from 8 kV to 20 kV,
The method of manufacturing a metal oxide nanowire array that the time is 5 minutes to 20 minutes. 7. The method of claim 6,
The manufacturing method of the metal oxide nanowire array,
Further comprising the step of transferring the prepared nanofiber film on a substrate,
The forming of the metal oxide coating layer is a method of manufacturing a metal oxide nanowire array made on the nanofiber film supported on the substrate. 7. The method of claim 6,
The manufacturing method of the metal oxide nanowire array,
Further comprising the step of manufacturing a laminated nanofiber film by laminating a plurality of the nanofiber film,
The metal oxide coating layer is formed on the laminated nanofiber film,
80% (number) to 100% (number) of the nanofibers included in the laminated nanofiber film are laminated to be aligned at an orientation angle of -45 degrees to +45 degrees with respect to the average orientation angle of the nanofibers metal oxide Methods of manufacturing nanowire arrays. 7. The method of claim 6,
The step of forming the metal oxide coating layer,
forming a metal oxide nanoparticle seed on the nanofiber film, and
Metal oxide nanowire comprising the step of immersing the nanofiber film in a solution containing a metal oxide precursor, and then synthesizing the nanofiber film at a temperature of 80 ° C. to 120 ° C. for 6 hours to 12 hours to grow the metal oxide A method of making an array. 7. The method of claim 6,
The manufacturing method of the metal oxide nanowire array,
Laminating a plurality of nanofiber films to prepare a laminated nanofiber film; and
Further comprising the step of transferring the laminated nanofiber film on a substrate,
The nanofiber film is a nanofiber film in a free support state,
The metal oxide coating layer is formed on the laminated nanofiber film,
80% (number) to 100% (number) of the nanofibers included in the laminated nanofiber film are laminated to be aligned at an orientation angle of -45 degrees to +45 degrees with respect to the average orientation angle of the nanofibers metal oxide Methods of manufacturing nanowire arrays.

Images