Patent Application
20080075939
Example embodiments will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings.
It should be noted that these Figures are intended to illustrate the general characteristics of methods, structure and/or materials utilized in certain example embodiments and to supplement the written description provided below. These drawings are not, however, to scale and may not precisely reflect the precise structural or performance characteristics of any given embodiment, and should not be interpreted as defining or limiting the range of values or properties encompassed by example embodiments. For example, the relative thicknesses and positioning of molecules, layers, regions and/or structural elements may be reduced or exaggerated for clarity. The use of similar or identical reference numbers in the various drawings is intended to indicate the presence of a similar or identical element or feature.
Example embodiments will now be described in greater detail with reference to the accompanying drawings. In the drawings, the thicknesses and widths of layers are exaggerated for clarity. Example embodiments may, however, be embodied in many different forms and should not be construed as limited to the example embodiments set forth herein. Rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of example embodiments to those skilled in the art.
It will be understood that when an element or layer is referred to as being “on”, “connected to” or “coupled to” another element or layer, it can be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of example embodiments.
Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context: clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of example embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of example embodiments.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
As used herein, the term “layered nanostructure” describes a nanostructure that has a layered structure where a nanomaterial is uniformly coated on the surface of a nanostructure as a nano-scale support. The shape of the nanostructure as a nano-scale support is not particularly limited in the present invention and examples thereof include nanoparticles and nanowires.
Example embodiments are directed to a method for preparing layered nanostructures by uniformly coating a nanomaterial on a nanostructure under multibubble sonoluminescence conditions.
Multibubble sonoluminescence is one of practical applications of sonoluminescence and is designed to substantially simultaneously generate a great deal of bubbles by irradiation of high-energy sonic waves and emit light upon growth and collapse of the bubbles.
Multibubble sonoluminescence spectra consist of continuous parts and peaks. The peaks are believed to be caused by electron transition of solvent molecules contained in bubbles. In addition, upon collapse of bubbles, a high-temperature (i.e. about 1,000° C.) high-pressure (i.e. about 500 bar) liquid zone is formed around the bubble walls on which multibubble sonoluminescence occurs, and hydroxyl (—OH) groups are produced in the liquid zone. Owing to high reactivity, the hydroxyl groups oxidize organic metals and involve high-energy chemical reactions which decompose contaminants in water. Sonochemical reactions under multibubble sonoluminescence conditions have advantages of rapid reaction time and efficient production of desired materials, as compared to sonochemical reactions under simple ultrasonic waves.
The nano-scale support is not particularly limited in example embodiments, but may be selected from metal oxide particles with a diameter of 50 nm or less. Examples of the metal oxide particles include, but are not limited to TiO2, ZnO, ZrO, Al2O3Fe2O3, Fe3O4, Ga2O3, SnO2, Sb2O3, SiO2, MnO2, NiO2 and mixtures thereof.
The nanomaterial coated on the nano-scale support is not particularly limited, but may be selected from metal chalcogenide including metal sulfide, metal selenide and metal telluride. Examples of the metal chalcogenide include, but are not limited to CdS, ZnS, HgS, PbS, InS, AgS, CuS, CdSe, ZnSe, HgSe, PbSe, InSe, AgSe, CuSe, CdTe, ZnTe, HgTe, PbTe, InTe, AgTe, CuTe and a mixture thereof.
In example embodiments of the present invention, the multibubble sonoluminescence conditions used to prepare the layered nanostructure are defined as a state in which a pressure of 1 to 2 atm is maintained via introduction of an inert gas into a reactor and a constant temperature of 20 to 70° C. is kept, within ultrasonic frequency and power bands at which multibubble sonoluminescence occurs.
The multibubble sonoluminescence used in the present invention employs sonoluminescence which is a light emission phenomenon upon collapse of ultra-fine (˜10 μm) bubbles oscillating at a ultrasonic wavelength, while taking into consideration the fact that when bubbles inside a solvent are oscillated by ultrasonic wave, the sonoluminescence is stably maintained even under an inner pressure (1 to 2 atm) of the solvent. The reactor inner pressure is 1 to 2 atm, more preferably, 1.40 to 1.45 atm.
Under the multibubble sonoluminescence conditions, metal chloride, a chalcogen element precursor and metal oxide are mixed with a solvent in the reactor, and metal chalcogenide is uniformly in-situ coated on metal oxide as a nano-scale support, to obtain a layered nanostructure. Of the metal chloride, the chalcogen element precursor and the metal oxide which are mixed with the solvent in the reactor, the metal oxide (the nano-scale support) is insoluble in the solvent, but the metal chloride and the chalcogen element precursor are ionized when an ultrasonic wave is applied, and are then reacted with each other to produce metal chalcogenide. The ultrasonic wave applied induces the reaction, allowing the metal chalcogenide to be coated on the surface of the metal oxide.
The ultrasonic frequency and power bands, at which multibubble sonoluminescence occurs, are in the range of 10 to 20 khz and 100 to 220 W, respectively. The reactor is not particularly limited in the present invention, but may be a glass or quartz reactor. Examples of the inert gas that may be used herein include, but are not limited to argon, nitrogen and helium gases. The reaction may be carried out at room temperature, preferably, at 20 to 70° C.
As the solvent, distilled water, alcohol or the like may be used herein, but the use of a highly volatile solvent such as methylene chloride, acetone or the like is not preferable.
During the coating under the multibubble sonoluminescence conditions, the ultrasonic wave reaction is preferably carried out for 20 to 30 min. When the ultrasonic wave reaction time is shorter than 20 min, the metal chalcogenide is incompletely produced. For this reason, the metal chalcogenide is not sufficiently coated on the metal oxide surface and the size of the nanostructure formed is non-uniform. On the other hand, the ultrasonic wave reaction time longer than 20 min is undesirable in that the coating is peeled away or the reaction has been already completed.
In the preparation method of the layered nanostructure employing multibubble sonoluminescence of the present invention, the thickness of the nanomaterial coated on the nano-scale support finally produced depends on a concentration ratio between initial reactants. As a result, the thickness of the layered nanostructure can be adjusted to a desired level.
According to example embodiments of the present invention, the metal chloride and the chalcogen element precursor as initial reactants are mixed in a mole ratio of 1:1. Examples of the metal chloride include cadmium chloride, zinc chloride, mercury chloride and the like. Examples of the chalcogen element precursor include thioacetamide, sodium sulfide, dithiocarbamate, sodium thiosulfate, diselenoacetamide, sodium selenide, diselenocarbamate and sodium selenate.
At this time, the metal chloride and the chalcogen element precursor as initial reactants are in situ reacted under multibubble sonoluminescence conditions to produce metal chalcogenide with a composition ratio of 1:1, and examples of the metal chalcogenide include CdS, ZnS, HgS, PbS, InS, AgS, CuS, CdSe, ZnSe, HgSe, PbSe, InSe, AgSe, CuSe, CdTe, ZnTe, HgTe, PbTe, InTe, AgTe and CuTe. Then, layered nanoparticles, where the metal chacogenide is coated on the metal oxide surface, are obtained as final products.
Since the reaction concentration ratio of the metal oxide to the metal chalcogenide is in a range of 3:1 to 5:1, the finally-coated thickness ratio of the metal chalcogenide:the metal oxide is adjusted to the range of 1:10 to 1:5.
According to example embodiments of the present invention, in preparation of layered nanoparticles, where the metal chalcogenide are coated on the metal oxide surface, when the reaction concentration ratio of the metal oxide to the metal chalcogenide is lower than 3:1, the metal chalcogenide is coated to an excessively thin thickness smaller than 2 nm on the metal oxide surface. On the other hand, when the reaction concentration ratio exceeds 5:1, a relatively large amount of the metal chalcogenide is produced. As a result, there is a risk that metal chalcogenide is uncoated on the metal oxide and these two materials are thus present in the form of particles.
Accordingly, since the metal chloride is in situ mixed with the chalcogen element precursor in a reaction mole ratio of 1:1 and the metal chalcogenide and the metal oxide are mixed in a reaction concentration ratio of 3:1 to 5:1, the coated thickness ratio of the metal chalcogenide:the metal oxide can be adjusted to the range of 1:10 to 1:5.
According to the method of example embodiments, it is possible to reproductively prepare a pure layered nanostructure where a nanomaterial is uniformly coated to a desired thickness on the surface of a nano-support.
Example embodiments of the present invention are directed to a layered nanostructure prepared by the method, the layered nanostructure having a structure in which a nanomaterial is coated on a nano-support.
In other example embodiments, the nano-scale support is not particularly limited, but may be selected from metal oxide with a size of 50 nm or less. Examples of the metal oxide include, but are not particularly limited to TiO2, ZnO, ZrO, Al2O3, Fe2O3, Fe3O4, Ga2O3, SnO2, Sb2O3, SiO2, MnO2, NiO2 and a mixture thereof.
The nanomaterial coated on the nano-scale support is not particularly limited, but may be selected from metal chalcogenide including metal sulfide, metal selenide and metal telluride. Examples of the metal chalcogenide include, but are not limited to CdS, ZnS, HgS, PbS, InS, AgS, CuS, CdSe, ZnSe, HgSe, PbSe, InSe, AgSe, CuSe, CdTe, ZnTe, HgTe, PbTe, InTe, AgTe, CuTe and mixtures thereof.
Any nano-scale support may be used without particular limitation so long as it has a nano-scale diameter. The nanomaterial is coated to a thickness of 2 to 30 nm on the nano-scale support.
Other example embodiments of the present invention are directed to layered nanoparticles, in which metal chalcogenide is coated on the surface of metal oxide. It is undesirable that the thickness of the metal chalcogenide in layered nanoparticles exceeds 30 nm, since the metal chalcogenide is excessively clustered and is thus not coated on the metal oxide surface.
Hereinafter, example embodiments will be explained in more detail with reference to the following examples. However, these examples are given for the purpose of illustration and are not to be construed as limiting the scope of example embodiments.
Distilled water was prepared as a solvent in a glass container of an ultrasonic generator, and cadmium chloride of 6.3 mmol, thioacetamide of 6.3 mmol and TiO2 (1.25 mmol, diameter: 20 nm) were added thereto. The mixture was reacted with each other with ultrasonic irradiation. At this time, an ultrasonic frequency and an ultrasonic power were 20 kHz and 220 W, respectively, an argon (Ar) gas was introduced into the glass container and a constant temperature reactor was maintained at a temperature of 50° C., to secure multibubble sonoluminescence conditions. Then, ultrasonic irradiation was carried out for 20 min. The resulting product was separated using a centrifuge, recrystallized, dried at room temperature and dried in a dry oven for about 10 hours, to prepare layered-nanoparticles where CdS was uniformly coated to a thickness of 25 to 30 nm on the surface of TiO2 (hereinafter, referred to as “CdS-coated TiO2 nanoparticles”).
Layered nanoparticles were prepared where ZnS was uniformly coated to a thickness of 2 nm on the surface of TiO2 (hereinafter, referred to as “ZnS-coated TiO2 nanoparticles”) in the same manner as in Example 1, except that zinc chloride of 3.75 mmol was used instead of cadmium chloride. Then, the nanoparticles were washed several times with a solvent such as distilled water, ethanol or acetone without using any centrifuge and were then recrystallized.
Layered nanoparticles were prepared where HgS was uniformly coated to a thickness of 2 nm on the surface of TiO2 (hereinafter, referred to as “HgS-coated TiO2 nanoparticles”) in the same manner as in Example 1, except that mercury chloride of 3.75 mmol was used instead of cadmium chloride and thioacetamide was used in an amount of 3.75 mmol. Then, the nanoparticles were washed several times with a solvent such as distilled water, ethanol or acetone without using any centrifuge and were thus recrystallized.
Layered nanoparticles we re prepared where CdS was uniformly coated to a thickness of 2 nm on the surface of TiO2 in the same manner as in Example 1, except that cadmium chloride was used in an amount of 3.75 mmol.
With respect to the layered nanoparticles prepared in Examples 1 to 3, the structures of thin films were observed using an X-ray diffractometer (XRD, Scintag XDS-2000).
The positions, at which the peaks of the CdS-coated TiO2 nanoparticles are plotted, are identical to the cases of nano-scale CdS and TiO2 alone. The peak thicknesses of the CdS-coated TiO2 nanoparticles were observed to be larger than those of the CdS and TiO2. That is, the relatively low intensities of peaks are assumed to arise from the fact that the particles are nano-scaled and the CdS is thinly coated on the surface of TiO2.
In addition, energy dispersive X-ray (EDX) spectroscopy analyses reveal that the atomic percents of Cd, S and Ti are 12.19%, 14.43%, and 72.09%, respectively. It was confirmed from this result that the composition ratio of Cd/S was nearly 1:1, the nanoparticles were prepared according to a reaction concentration ratio of CdS:TiO2=5:1 and the thickness ratio of CdS/TiO2 was 1:5.
In addition, energy dispersive X-ray (EDX) spectroscopy analyses of the ZnS-coated TiO2 nanoparticles reveal that the atomic percents of Zn, S and Ti are 12.50%, 9.45%, and 79.05%, respectively. It was confirmed from this result that the composition ratio of Zn/S was nearly 1:1 and the thickness ratio of ZnS/TiO2 was 1:7.
In addition, energy dispersive X-ray (EDX) spectroscopy analyses of the HgS-coated TiO2 nanoparticles reveal that the atomic percents of Hg, S and Ti are 13.59%, 8.48%, and 77.93%, respectively. It was confirmed from this result that the composition ratio of Hg/S was nearly 1:1 and the thickness ratio of HgS/TiO2 was 1:6.
With respect to the layered-nanoparticles prepared in Examples 1 to 3, the structures of thin films were observed using transmission electron microscopy (TEM, JEOL, JEM-2000EXII) and high resolution X-ray diffractometer (HR-TEM, JEOL, JEM-3010).
In a case where nanoparticles are obtained under the conditions that a reaction concentration ratio of TiO2 to ZnS or HgS was 3:1, the ZnS or HgS was coated to a small thickness (i.e. about 2 nm) on the TiO2 surface.
According to the method of example embodiments of the present invention, it can be confirmed that nano-materials were uniformly coated to a nano-scale thickness on the surface of nanoparticles prepared under the multibubble sonoluminescence conditions.
Although example embodiments have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications and variations are possible, without departing from the scope and spirit of the appended claims. Accordingly, such modifications and variations are intended to come within the scope of the claims.
As apparent from the above description, the method for preparing layered nanostructures of example embodiments may include uniformly coating a nanomaterial to a desired thickness on a nano-scale support under multibubble sonoluminescence conditions. Layered nanostructures, where a nanomaterial is uniformly coated to a desired thickness on a nano-scale support, can be obtained by the method. Furthermore, the use of the method realizes reproductive preparation of uniform layered nanostructures at a relatively low temperature and rapid speed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2006-0092837 | Sep 2006 | KR | national |
| 10-2007-0061142 | Jun 2007 | KR | national |
