Method for preparing nanostructure by electrochemical deposition, and nanostructure prepared thereby

Abstract

The present invention relates to a method for preparing a nanostructure by electrochemical deposition, and a nanostructure prepared thereby, and more specifically, to: a method for preparing a nanostructure by electrochemical deposition, wherein it is possible to prepare a nanostructure having remarkable morphological, structural and optical characteristics by controlling a method for applied power during electrochemical deposition; and a nanostructure prepared thereby.

Claims

1. A method of forming a nanostructure by electrochemical deposition, comprising: positioning a plurality of electrodes which includes a working electrode in a growth solution in an electrolytic deposition reactor; growing a first nanostructure on the working electrode by supplying a first applying power source between the plurality of electrodes for a first applying time and supplying oxygen/inert gas into the electrolytic deposition reactor; and growing a second nanostructure on the first nanostructure grown on the working electrode by supplying a second applying power source between the plurality of electrodes for a second applying time and supplying oxygen/inert gas into the electrolytic deposition reactor, wherein the first applying power source and the second applying power source are different from each other, wherein the first applying power source is in a range of 0.8 to 1.2 V and the first applying time is in a range of 6 to 240 seconds, wherein the second applying power source is in a range of 0.5 to 0.8 V and the second applying time is in a range of 900 to 1,500 seconds, and wherein the growing of the first nanostructure and the growing of the second nanostructure are performed at a temperature in a range of 80 to 100 C.

2. The method of claim 1, wherein the working electrode is a conductive substrate, and is a transparent substrate on which a transparent conductive film is formed.

3. The method of claim 2, wherein the transparent substrate is a glass substrate, and the transparent conductive film is formed of a material selected from the group consisting of ITO, ILO, ATO, ZnO, CdO, SnO.sub.2, and In.sub.2O.sub.3.

4. The method of claim 1, wherein the plurality of electrodes include a reference electrode, a counter electrode, and the working electrode, and the reference electrode is formed of Ag/AgCl and the counter electrode is formed of a material selected from the group consisting of Pt, Au, Zn, and Ag.

5. The method of claim 1, wherein the growth solution is an electrolyte solution including metal salts, and the metal is zinc (Zn).

6. The method of claim 5, wherein the growth solution is a ZnCl.sub.2 or Zn(NO.sub.3).sub.2 aqueous solution having a concentration in a range of 0.0001 to 0.01 M.

7. The method of claim 6, wherein the growth solution further includes potassium chloride (KCl).

8. The method of claim 1, further comprising performing a heat treatment at a temperature in a range of 250 to 350 C. after growing the second nanostructure.

9. The method of claim 1, further comprising applying additional applying power source n times (n is 1 or more) after applying the second applying power source.

10. A nanostructure prepared by the method of claim 1.

11. The nanostructure of claim 10, wherein the nanostructure is a zinc oxide nanorod.

12. The nanostructure of claim 10, wherein the nanostructure has an average diameter in a range of 50 to 160 nm.

Description

DESCRIPTION OF DRAWINGS

(1) FIGS. 1 to 3 show FE-SEM measurement results of nanostructures prepared according to Examples of an embodiment of the present invention and Comparative Examples.

(2) FIG. 4 shows measurement results of the diameter and density of a nanostructure prepared according to an embodiment of the present invention.

(3) FIGS. 5 and 6 show XRD measurement results of a nanostructure prepared according to the embodiment of the present invention.

(4) FIGS. 7 to 10 show photoluminescence (PL) measurement results of a nanostructure prepared according to the embodiment of the present invention.

MODES OF THE INVENTION

(5) Hereinafter, the present invention will be described in detail with reference to embodiments. However, the present invention is not limited to the following embodiments.

Example

Preparation of Zinc Oxide Nanostructure

(6) A zinc oxide nanostructure was prepared using a potentiostat/galvanostat (Model PL-9 Physio Lab Co., Ltd., South Korea) as an electrochemical deposition device and using a three-electrode system. ITO/glass (sheet resistance: 10 /sq) was used as a working electrode, a Pt-mesh was used as a counter electrode, Ag/AgCl (1 M KCl) was used as a reference electrode, and ITO/glass which was the working electrode was used after cleaning with ultrasonic waves in acetone, methanol, and deionized water for 10 minutes respectively, and drying with filtered air.

(7) As an electrolyte solution in which a zinc oxide nanostructure is grown, 0.005 M ZnCl.sub.2 (Sigma-Aldrich Co. LLC., purity>98%) was used as a main electrolyte solution for Zn.sup.2, and 0.1 M KCl (KANTO KAGAKU, purity>99.5%) was used as an auxiliary electrolyte solution. A bath temperature was set to 90 C., a mixed gas of Ar/O.sub.2 which is an oxygen source was introduced into the solution for 10 minutes, and thereby an electrolyte solution saturated with the mixed gas of Ar/O.sub.2 was prepared and used. A first applied electric potential and time, and a second applied electric potential and time were changed as shown in the following Table 1 such that total process time was 1,200 seconds, and thereby a zinc oxide nanostructure was synthesized.

(8) After the electrochemical process, a heat treatment was performed at 300 C. under a nitrogen atmosphere for 1 hour using a rapid thermal process (RTP).

(9) TABLE-US-00001 TABLE 1 First-step Deposition Second-step Deposition No potential (V) time (s) potential (V) time (s) 1 1.2 3 0.7 1197 2 6 1194 3 10 1190 4 20 1180 5 60 1140 6 240 960 7 1 10 1190 8 20 1180 9 60 1140 10 240 960 11 0.8 10 1190 12 20 1180 13 60 1140 14 240 960 15 0.6 10 1190 16 20 1180 17 60 1140 18 240 960 19 0.4 10 1190 20 20 1180 21 60 1140 22 240 960 23 0.2 10 1190 24 20 1180 25 60 1140 26 240 960

Comparative Example

(10) A zinc oxide nanostructure was grown while a constant voltage was applied for 1,200 seconds without a change in the voltage.

Experimental Example

Field Emission Scanning Electron Microscope (FE-SEM) Measurement

(11) FE-SEM pictures were taken to determine the morphological characteristics of the zinc oxide nanostructure according to the magnitude and the applying time of the first applied voltage, and are shown in FIGS. 1 to 3.

(12) FIG. 1 shows FE-SEM pictures of the zinc oxide nanostructure prepared while the amount and applying time of the first applied voltage were changed, where FIGS. 1(A) to 1(X) show the zinc oxide nanostructures prepared while the first applied voltages of 1.2, 1.0, 0.8, 0.6, 0.4, and 0.2 V were applied for 10, 20, 60, and 240 seconds each, and then the second applied voltages of 0.7 V were applied for 1190, 1180, 1140, and 960 seconds each, and FIG. 1(Y) shows the zinc oxide nanostructures prepared while the first applied voltage of 1.5 V was applied for 10 seconds, and then the second applied voltage of 0.7 V was applied for 1,190 seconds.

(13) As shown in FIG. 1, when the first applied voltage is 0.8 V or more, it may be determined that the zinc oxide nanostructures having a high density were prepared. This is because the electron density of the surface of the substrate (working electrode), which is required to form an instantaneous nucleation site, was sufficiently supplied when a voltage of 0.8 V or more was applied.

(14) When the second applied voltage of 0.7 V was applied for 1,190 seconds after the first applied voltage of 1.5 V was applied for 10 seconds, a zinc oxide nanostructure having a hexagonal crystal structure was grown. However, when the first applied voltage was applied for 20 seconds or more, a reference electrode was ruined.

(15) In FIG. 2, FIGS. 2(A) to 2(F) show top-views of zinc oxide nanostructures prepared while the first applied voltage of 1.2 V was applied for 3, 6, 10, 20, 60, and 240 seconds each, and then the second applied voltage of 0.7 V was applied for 1197, 1194, 1190, 1180, 1140, and 960 seconds each, and FIG. 2(G) shows cross-sectional views of zinc oxide nanostructures prepared while the first applied voltage of 1.2 V was applied for 10 seconds, and then the second applied voltage of 0.7 V was applied for 1,190 seconds.

(16) As shown in FIG. 2, when the zinc oxide nanostructures were prepared while the first applied voltage of 1.2 V was applied for 10 seconds, and then the second applied voltage of 0.7 V was applied for 1,190 seconds, it may be determined that the zinc oxide nanostructures having a height of about 550 nm were grown.

(17) FIG. 3 shows a result of FE-SEM picture measurement of zinc oxide nanostructures prepared in Comparative Example, FIGS. 3(A) to 3(E) show top-views of zinc oxide nanostructures prepared while applied voltages of 1.2, 1.0, 0.8, 0.7, and 0.6 V were applied continuously for 1,200 seconds each, and FIG. 3(F) shows cross-sectional views of zinc oxide nanostructures prepared while the applied voltage of 0.7 V was applied.

(18) As shown in FIG. 3, when the constant amount of the applied voltage was continuously applied, it may be determined that the zinc oxide nanostructures were not grown to be perpendicular.

Experimental Example

Measurement of Diameter and Density of Nanostructure

(19) The diameter and density of the zinc oxide nanostructures prepared while the first applied voltage of 1.2 V was applied for 3, 6, 10, 20, 60, and 240 seconds each, and then the second applied voltages of 0.7 V was applied for 1197, 1194, 1190, 1180, 1140, and 960 seconds each, were measured using FE-SEM pictures in FIG. 2, and are shown in FIG. 4.

(20) As shown in FIG. 4, when the applying time of the first applied voltage increased, the diameter of the zinc oxide nanostructures had a tendency to decrease and then increase again, and when the applying time of the first applied voltage increased, the density of the zinc oxide nanostructures had a tendency to increase and then decrease again. From these results, it may be determined that the diameter and density of the zinc oxide nanostructures showed an opposite tendency as the applying time of the first applied voltage increased.

Experimental Example

X-Ray Diffraction Analysis (XRD)

(21) An XRD was measured to determine the structural characteristics of the zinc oxide nanostructure, and results are shown in FIGS. 5 and 6.

(22) FIG. 5(A) is a result of an XRD measurement of zinc oxide nanostructures prepared while the first applied voltage of 1.2 V was applied while the applying time was changing from 3 to 240 seconds, and then the second applied voltage of 0.7 V was applied while the applying time was changing from 1,197 to 960 seconds. FIGS. 5(B) and 5(C) are results of an XRD measurement of zinc oxide nanostructures prepared while the application of the first applied voltage was changing from 1.0 to 0.8 V while the applying time was changing from 10 to 240 seconds, and then the second applied voltage of 0.7 V was applied while the applying time was changing from 1,190 to 960 seconds. FIG. 5(D) is a result of an XRD measurement of zinc oxide nanostructures prepared while the application of the first applied voltage was changing from 0.2 to 1.5 V while applied for 10 seconds, and then the second applied voltage of 0.7 V was applied for 1,190 seconds.

(23) As shown in FIG. 5, the zinc oxide nanostructures according to the embodiment of the present invention showed (100) peaks at 31, and thus, it may be determined that all the zinc oxide nanostructures included polycrystalline zinc oxide nanorods.

(24) FIG. 6 shows a result of a measurement of a (002) peak intensity at 34, a (100) peak intensity at 31, and the intensity ratio between (002)/(100) peaks according to the amount and the applying time of the first applied voltage.

(25) As shown in FIG. 6(A), it may be determined that, when the first applied voltage was 0.8 V or more, the (002) peak intensity increased, and when the applying time was 10 seconds, the highest peak strength was shown.

(26) FIGS. 6(B) and 6(C) show the (002) peak intensity, the (100) peak intensity, and the intensity ratio between (002)/(100) peaks of the nanostructures prepared while the first applied voltage of 1.2 V was applied and the applying time was changed, and it may be determined that the peak strength of (002) peak increased until 10 seconds, but the peak strength of (002) peak decreased after 10 seconds. This is because the electron density to form an instantaneous nucleation site was insufficient until 10 seconds, but the electron density was excessive after 10 seconds. The greater the intensity ratio between (002)/(100) peaks is, the more nanorods were grown in a c-axis direction which is in a direction perpendicular to a substrate, and it may be determined that the intensity ratio between (002)/(100) peaks also had a tendency to increase until 10 seconds, but decrease after 10 seconds.

Experimental Example

Measurement of Optical Properties According to First Applied Voltage

(27) The photo luminescence (PL) characteristics of zinc oxide nanostructures prepared while the first applied voltage was changing from 0.2 to 1.5 V was applied for the constant applying time of 10 seconds, and then the second applied voltage of 0.7 V was applied for 1,190 seconds were measured and are shown in FIG. 7. The intensity of a weak near-band edge emission (NBE) peak positioned in an ultraviolet region, the intensity of a strong deep-level emission (DLE) peak positioned in a visible region, and the intensity ratio between the NBE and DLE peaks are shown in FIG. 8.

(28) In general, the NBE peak results from free exciton recombination, and the DLE peak results from defects such as oxygen vacancy, zinc vacancy, interstitial oxygen, and interstitial zinc.

(29) As shown in FIG. 8(A), the NBE peak intensity when the first applied voltage of 1.0 V was applied was 126,101, which was higher than the intensity of the NBE peak when the first applied voltage of 1.2 V was applied (118,170), and the DLE peak intensity was also measured to be higher when the first applied voltage of 1.0 V was applied, and accordingly, the value of the intensity ratio between the NBE and DLE peaks are shown to be highest when the first applied voltage of 1.2 V was applied. As shown in FIGS. 8(A) and 8(B), when the first applied voltages of 1.5, 1.2, 1.0, 0.8, 0.7, 0.6, 0.4, and 0.2 V were applied, the intensity values of the DLE peak were respectively 2,767, 1,491, 2,808, 5,020, 3,240, 4,087, 6,230, and 3,874, and thus, it may be determined that the intensity value of the DLE peak was lowest when the first applied voltages of 1.2 V was applied. The values of the intensity ratio between NBE/DLE peaks were respectively 4.2, 79.26, 44.92, 13.11, 41.95, 16.72, 4.44, and 25.18 when the above-described values of the first applied voltages were applied, and thus, it may be determined that the intensity ratio between NBE/DLE peaks was highest when the first applied voltages of 1.2 V was applied.

Experimental Example

Measurement of Optical Properties According to Applying Time of First Applied Voltage

(30) The photo luminescence (PL) characteristics of the zinc oxide nanostructures prepared while the constant first applied voltage of 1.2 V was applied while the applying time was changing from 3 to 240 seconds, and then the second applied voltage of 0.7 V was applied while the applying time was changing from 1,197 to 960 seconds were measured and are shown in FIG. 9. The NBE peak intensity, the DLE peak intensity, and the intensity ratio between the NBE and DLE peaks are shown in FIG. 10.

(31) As shown in FIG. 10, when the applying times were 3, 6, 10, 20, 60, and 240 seconds, the values of the NBE peak intensity were respectively 41,611, 49,764, 118,170, 30,320, 62,128, and 57,821, and thus, it may be determined that the intensity value of the NBE peak was highest when the applying time was 10 seconds. The values of the DLE peak intensity were respectively 2,219, 1,942, 1,490, 1,653, 2,270, and 4,733 when the above-described applying times were used, and thus, it may be determined that the value of the DLE peak intensity was lowest when the applying time was 10 seconds. Further, the values of the intensity ratio between the NBE and DLE peaks were respectively 18.8, 25.7, 76.3, 18.4, 27.4, and 12.3 when the above-described applying times were used, and thus, it may be determined that the value of the intensity ratio between the NBE and DLE peaks was highest when the applying time was 10 seconds.

INDUSTRIAL APPLICABILITY

(32) In the method of preparing a nanostructure by electrochemical deposition according to the embodiment of the present invention, a buffer layer and an additive are not used, a power applying method is optimized in electrochemical deposition, and thereby a nanostructure having excellent morphological, structural and optical characteristics can be prepared.