Nanostructured thin film and method for controlling surface properties thereof

Disclosed herein is a nanostructured thin film. The nanostructured thin film comprises a nanoparticle layer and a number of micro-undulated surfaces formed on the nanoparticle layer. The two micro-undulated structures of the nanostructured thin film are uniformly introduced over a large area. This configuration makes it easy to control the surface properties of the nanostructured thin film. Therefore, the nanostructured thin film can be widely applied to a variety of devices. Also disclosed herein is a method for controlling the surface properties of the nanostructured thin film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims priority under U.S.C. §119 to Korean Patent Application No. 2008-66639, filed on Jul. 9, 2008, the entire contents of which is incorporated herein in its entirety by reference.

BACKGROUND

This disclosure is directed to a nanostructured thin film and a method for controlling the surface properties of the nanostructured thin film. More specifically, the nanostructured thin film comprises a nanoparticle layer including a number of nanoparticles and micro-undulated surfaces formed on the nanoparticles.

2. Description of the Related Art

In general, the electrical, magnetic, optical and chemical properties of quantum-sized materials differ significantly from those of the corresponding macroscopic materials. Due to these differences, quantum-sized materials exhibit various interesting chemical and physical properties, such as melting point depression, metal-insulator transition, single electron tunneling and near-field optical properties. In addition, the physical properties of nanometer-sized materials are intimately associated with their regular two- or three-dimensional arrangement. To accurately understand the physical properties of nanometer-sized materials, there is a need to develop a model whose structural or spatial regularity is well defined.

Furthermore, the luminescent properties, electrical properties, optical properties and physical properties of nanostructures can be controlled by varying the size and composition of the nanostructures. Based on these characteristics, nanostructures are becoming increasingly important in the development of sub-micron sized, high-integration and high-performance circuits and sensors, ultrahigh-density data storage media, optical devices and electrical devices. Under these circumstances, research on nanostructures is actively underway for a variety of applications. Thus, there is a need to develop a nanostructured thin film whose physicochemical properties are easily controllable and that is easy to produce.

SUMMARY

In an embodiment, a nanostructured thin film is disclosed, which comprises a nanoparticle layer including a number of nanoparticles and micro-undulated surfaces formed on the nanoparticles.

The micro-undulated surfaces may be smaller in size than the nanoparticles.

The nanoparticles may have a single or core-shell double structure composed of an inorganic material, a metal, a semiconductor or a polymer; and the micro-undulated surfaces may include a metal oxide, a metal nitride, a metal carbide, etc.

The nanostructured thin film is applicable to a variety of microfluidic devices because its surface energy, optical properties and electrical properties can be controlled in an easy manner.

In another embodiment, a method for controlling the surface properties of a nanostructured thin film is disclosed, which comprises forming a nanoparticle layer including a number of nanoparticles and forming a number of micro-undulated surfaces having a size smaller than that of the nanoparticles on the nanoparticles.

The nanoparticle layer may be formed by applying inorganic material, metal, semiconductor or polymer nanoparticles to a substrate by colloidal lithography; and the micro-undulated surfaces may be formed using a metal oxide, a metal nitride or a metal carbide by a chemical vapor deposition process, a physical vapor deposition process, such as RF magnetron sputtering, DC magnetron sputtering, ion/e-beam sputtering or pulsed laser deposition, or an atomic layer deposition process.

According to the method, the surface properties (e.g., surface energy and optical properties) of the nanostructured thin film on a large area can be controlled as intended.

In another embodiment, an electronic device is disclosed, which comprises the nanostructured thin film.

DETAILED DESCRIPTION

Hereinafter, a detailed description will be given of exemplary embodiments with reference to the accompanying drawings.

It will be understood that when an element or layer is referred to as being “on,” “interposed,” “disposed,” or “between” another element or layer, it can be directly on, interposed, disposed, or between the other element or layer or intervening elements or layers may be present.

In an embodiment, a nanostructured thin film is provided wherein the nanostructured thin film comprises a nanoparticle layer including a number of nanoparticles and micro-undulated surfaces formed on the nanoparticles.

The term “nanoparticle layer” used herein refers to a layer composed of a number of nanoparticles arranged adjacent to or spaced apart from one another to form a nanoscale undulated structure.

Surface energy control in thin films has drawn attention as a technology utilizing self-cleaning effects to prevent surface contamination and moisture infiltration in devices and touch screens. For example, when glass substrates for use in conventional flat panel displays are used as touch screens without any surface treatment, contaminants such as fingerprint residue may induce malfunction of the devices. In contrast, the surface energy of the nanostructured thin film can be controlled to change the surface state from hydrophilic to hydrophobic, or vice versa. This hydrophilic/hydrophobic surface control can be widely used to prevent display screens from contamination, to protect the surface of outdoor objects from ice and stains, and to fabricate microfluidic devices.

FIG. 1ais an exemplary schematic cross-sectional diagram illustrating the structure of the nanostructured thin film. Referring toFIG. 1a, the nanostructured thin film comprises a nanoparticle layer20including a number of nanoparticles and a number of micro-undulated surfaces30formed on the nanoparticle surface of the nanoparticle layer20. The nanoparticle layer20may have a monolayer or multilayer structure.

The micro-undulated surfaces30may be smaller in size than the nanoparticles. For example, the nanoparticles of the nanoparticle layer20may have a size of several tens of nanometers to several micrometers, and the micro-undulated surfaces30may have a size of several nanometers to several hundreds of nanometers. The sizes of the nanoparticles and the micro-undulated surfaces may also be in the micrometer range.

The micro-undulated surfaces30may be formed in a plural number. The micro-undulated surfaces30formed on the nanoparticles may have various shapes, for example, nanoflowers, nanotrees, nanobouquets, nanodots, nanobelts, nanoribbons, nanopyramids, nanowavys and nanocavities.

The nanoparticles may have a single or core-shell double structure composed of an inorganic material, a metal, a semiconductor or a polymer. For example, the nanoparticles20may include at least one material selected from the group consisting of gold, silver, chromium, molybdenum, nickel, cobalt, iron, titanium, ZnO, alumina, silicon and polystyrene.

The micro-undulated surfaces30may include a metal oxide, a metal nitride or a metal carbide. Examples of the metal oxide include, but are not necessarily limited to: TiO2, ZnO, CO3O4, CoO, SiO2, SnO2, WO3, Ta2O3, BaTiO3, BaZrO3, ZrO2, HfO2, Al2O3, Y2O3, ZrSiO4, Fe2O3, Fe3O4, CeO, CrO3, and mixtures thereof. The metal oxide may be a two-component system such as SiO2—ZrO2, SiO2—TiO2or TiO2—ZrO2, or a three-component system such as V2O5—SiO2—Nb2O5.

The nanoparticles of the nanoparticle layer20may be arranged adjacent to one another (FIG. 1a) or spaced apart from one another at regular intervals (FIG. 1b). By controlling the density of the nanoparticles, the wetting properties (hydrophobicity/hydrophilicity) and optical properties of the nanostructured thin film can be controlled.

Although not shown in the figures, the nanoparticle layer20may be formed patternwise on a substrate. Patterning of a nanostructure on a substrate is well known in the art.

The surface roughness and optical properties (e.g., refractive index and diffusion properties) of the nanostructured thin film can be controlled. The contact angle (θ) of a droplet on a solid surface is indicative of water repellency. Generally, the solid surface is evaluated to be water repellent (hydrophobic) when θ≧90°, highly water repellent when 110°≦θ≦150°, and superhydrophobic when θ>150°. As the roughness of the solid surface increases, the hydrophobicity of the solid surface increases. The contact angle of a flat hydrophobic surface is typically from 100° to 120°, whereas that of a rough surface or a finely rugged surface amounts to 160° to 170°. The surface properties of the nanostructured thin film can be controlled from superhydrophobicity to superhydrophilicity.

For additional functionalization, a material with low surface energy can be used to chemically modify the surface of the nanostructured thin film. Suitable materials are silane compounds and fluorinated polymers, and examples thereof include, but are not necessarily limited to: fluorinated silane compounds, such as 3,3,3-trifluoropropylsilane, tridecafluoro-1,1,2,2-tetrahydrooctylsilane, pentafluorophenylsilane, heptadecafluoro-1,1,2,2-tetrahydrodecylsilane, 3-heptafluoroisopropoxypropylsilane and trifluoroethylsilane; alkyl silane compounds containing methyl, ethyl, n-propyl, n-butyl, isobutyl, hexyl, hexadecyl, n-heptyl, n-octyl, n-octadecyl, dodecyl, decyl, pentyl, docosyl or bis(trimethylsilylmethyl) group; and silicone precursors, such as dimethyldimethoxysilane and dimethyldiethoxysilane.

Superhydrophobicity and superhydrophilicity are phenomena based on the same basic principle. That is, superhydrophobicity and superhydrophilicity are results obtained from simultaneous interaction of a micro- or nano-scale structure and a chemical composition of a surface. A hydrophilic surface having a micro- or nano-scale structure exhibits superhydrophilicity, and a hydrophobic surface having a micro- or nano-scale structure exhibits superhydrophobicity. In the exemplary embodiments, the two opposite phenomena based on the same principle can be optionally attained by simple processing. The nanostructured thin film has a structure in which the smaller micro-undulated surfaces formed on the larger nanoparticles have a double morphology. Due to this structure, the nanostructured thin film has a double morphology to achieve both superhydrophilicity and superhydrophobicity.

In the case of superhydrophobicity, the nanostructured thin film can be applied to barrier thin films, water-repellent coatings and self-cleaning coatings capable of preventing contamination by water or other contaminants. In the case of superhydrophilicity, a liquid containing biomolecules can be applied to the nanostructured thin film to form a completely flat layer without leaving any droplets. Furthermore, the nanostructured thin film can have a composite surface exhibiting both hydrophilicity and hydrophobicity. In this case, the nanostructured thin film is useful as a channel in a microfluidic device.

In another embodiment, a method for controlling the surface properties of a nanostructured thin film is provided.

According to the method, a nanoparticle layer is formed in which a number of nanoparticles are included to form an undulated structure, and then a number of micro-undulated surfaces having a size smaller than that of the nanoparticle layer are formed on the nanoparticles to produce a nanostructured thin film with an undulated surface bilayer structure. The surface energy, optical properties and electrical properties of the final nanostructured thin film can be controlled by varying various production parameters.

FIGS. 2 and 3show schematic diagrams for explaining methods for controlling the surface properties of nanostructured thin films. Referring toFIG. 2, first, a nanoparticle layer20including a number of nanoparticles is formed.

In the first step, the nanoparticle layer may be formed by applying inorganic material, metal, semiconductor or polymer nanoparticles to a substrate by colloidal lithography. For example, colloidal particles can be self-arranged on a substrate. An aqueous solution of the nanoparticles is applied to a substrate, followed by drying to self-arrange the nanoparticles on the substrate. The application can be performed by various processes, such as spin coating, dip coating, flow coating, doctor blade coating, dispensing, inkjet printing, offset printing, screen printing, pad printing and gravure printing.

Depending on the application process used, the application processing and the arrangement of nanoparticles may be varied. In the case of dip coating (FIG. 2), a substrate is cleaned, dipped in a dispersion of nanoparticles in water, taken from the dispersion, and dried to evaporate the water to form a high-density hexagonal close-packed structure in which the nanoparticles are regularly arranged. InFIG. 2, the left diagram shows the formation of micro-undulated surfaces with a nanoflower structure partially coated on a high-density cubic nanoparticle monolayer, and the right diagram shows the formation of micro-undulated surfaces with a nanowavy structure uniformly coated on a high-density cubic nanoparticle monolayer. On the other hand, in the case where a dispersion of the nanoparticles is applied by spin coating (FIG. 3), a substrate is treated with a charged polymeric electrolyte (optional), poly(allylamine hydrochloride) and polyacrylic acid, and then the dispersion is spin-coated at a medium rate on the substrate to uniformly disperse the nanoparticles at a low density. The nanoparticles may be formed into a monolayer or multilayer structure upon formation of the nanoparticle layer or micro-undulated surfaces. InFIG. 3, the left diagram of shows the formation of micro-undulated surfaces with a nanoflower structure partially coated on a low-density nanoparticle monolayer, and the right diagram shows the formation of micro-undulated surfaces with a nanowavy structure uniformly coated on a low-density nanoparticle monolayer.

The nanoparticles may have a single or core-shell double structure composed of an inorganic material, a metal, a semiconductor or a polymer. For example, the nanoparticles20may include at least one material selected from the group consisting of gold, silver, chromium, molybdenum, nickel, cobalt, iron, titanium, ZnO, alumina, silicon and polystyrene.

The micro-undulated surfaces may be formed by a vapor deposition process, RF magnetron sputtering or DC magnetron sputtering, an ion/e-beam sputtering process, a pulsed laser deposition process, or an atomic layer deposition process. The micro-undulated surfaces formed on the nanoparticles may have various shapes, for example, nanoflowers, nanotrees, nanobouquets, nanodots, nanobelts, nanoribbons, nanopyramids, nanowavys and nanocavities. Unlike in the prior art, the micro-undulated surfaces can be formed in a simple manner within 2 to 10 minutes at room temperature without the need for high-temperature processing.

The micro-undulated surfaces30may include a metal oxide, a metal nitride or a metal carbide. Examples of the metal oxide include, but are not necessarily limited to: TiO2, ZnO, CO3O4, CoO, SiO2, SnO2, WO2, Ta2O3, BaTiO3, BaZrO3, ZrO2, HfO2, Al2O3, Y2O3, ZrSiO4, Fe2O3, Fe3O4, CeO, CrO2, and mixtures thereof. The metal oxide may be a two-component system such as SiO2—ZrO2, SiO2—TiO2or TiO2—ZrO2, or a three-component system such as V2O5—SiO2—Nb2O5.

The surface properties of the nanostructured thin film can be controlled by varying the diameter and surface roughness of the nanoparticles. The surface of the nanostructured thin film can be chemically modified by using a low surface energy material, such as a silane compound or a fluorinated polymer. The nanostructured thin film treated with the low surface energy material exhibits superhydrophilicity by capillary action due to the micro-undulated surfaces. Examples of such low surface energy materials include: fluorinated silane compounds, such as 3,3,3-trifluoropropylsilane, tridecafluoro-1,1,2,2-tetrahydrooctylsilane, pentafluorophenylsilane, heptadecafluoro-1,1,2,2-tetrahydrodecylsilane, 3-heptafluoroisopropoxypropylsilane and trifluoroethylsilane; alkyl silane compounds containing methyl, ethyl, n-propyl, n-butyl, isobutyl, hexyl, hexadecyl, n-heptyl, n-octyl, n-octadecyl, dodecyl, decyl, pentyl, docosyl or bis(trimethylsilylmethyl) group; dimethyldimethoxysilane; and dimethyldiethoxysilane.

In yet another embodiment, an electronic device is provided which comprises the nanostructured thin film. Examples of the electronic device include, but are not necessarily limited to, LEDs, laser devices, memory devices, sensors and photovoltaic devices. The nanostructured thin film can also be applied to microfluidic devices. Further, the nanostructured thin film can be used to fabricate biosensors, such as DNA chips and physiological monitoring sensors, optical biosystems, bioelectronic devices, biological nanomachines, etc. Further, the nanostructured thin film is applicable to various functional coatings. Such functional coatings may be self-cleaning coatings, water repellent coatings, hydrophilic coatings or contamination-free coatings.

A better understanding of exemplary embodiments will be described in more detail with reference to the following examples. However, these examples are given merely for the purpose of illustration and are not to be construed as limiting the scope of the embodiments.

EXAMPLES

An aqueous solution (0.5 wt %) of SiO2nanoparticles (size=100 nm) was coated on a pre-cleaned silicon substrate (5 cm×5 cm) by dip coating to form a nanoparticle layer. In the nanoparticle layer, the nanoparticles were self-arranged due to the adhesive force of the nanoparticles. Subsequently, RF magnetron sputtering was performed for 10 minutes while controlling the flow rates of oxygen and argon gases to introduce micro-undulated surfaces composed of cobalt oxide on the nanoparticles, thereby completing the production of a nanostructured thin film.

150 ml of (tridecafluoro-1,1,2,2-tetrahydrooctyl)trimethoxysilane as a liquid precursor was deposited on the nanostructured thin film produced in Example 1 by chemical vapor deposition in a sealed reaction container at 100° C.

The contact angles of the nanostructured thin films produced in Examples 1 and 2 were measured (FIG. 4). Referring toFIG. 4, the contact angle of the nanostructured thin film produced in Example 1 (left) was almost zero, indicating superhydrophilicity, and the contact angle of the nanostructured thin film treated with the fluorinated compound produced in Example 2 (right) was 141°, indicating superhydrophobicity. These results demonstrate that the surface properties of the nanostructure could be controlled from superhydrophilicity to superhydrophobicity by the introduction of the hydrophobic groups into the surface of the nanostructure.

Comparative Example 1

Cobalt oxide was introduced on a pre-cleaned silicon substrate (5 cm×5 cm) to form a thin film. The contact angle of the thin film was measured. The thin film was treated with (tridecafluoro-1,1,2,2-tetrahydrooctyl)trimethoxysilane in the same manner as in Example 2. The contact angle of the treated thin film was measured (FIG. 5).

Referring toFIG. 5, the contact angles of the cobalt oxide-introduced thin film (left) and the thin film (right) treated with the hydrophobic fluorinated compound were 78° and 110°, respectively.

Experimental Example 1

FIGS. 6 and 7show SEM images of the nanostructured thin films produced in Example 1. InFIG. 6, the left dark portion represents the nanoparticles and the right bright portion represents the micro-undulated structure formed on the nanoparticle layer.FIG. 7is a surface SEM image of the high-density nanostructure produced in Example 1. Referring toFIG. 7, the micro-undulated surfaces were formed on the surface of the nanoparticles of the nanoparticle layer, and the nanoparticles were arranged in a hexagonal pattern to form a high-density packed structure, as marked in the image.

Although exemplary embodiments have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications and changes can be made in exemplary embodiments without departing from the spirit and scope of the invention. Therefore, the scope of the invention should be defined by the claims that follow.