JP4510550B2 - Method for controlling metal fine particle structure in metal fine particle thin film - Google Patents

Description

  The present invention relates to a method for producing a metal fine particle thin film, and in particular, the structure of the particle size, shape, arrangement, etc. of the metal fine particles in the metal fine particle thin film utilizing local surface plasmons can be controlled.

  In recent years, a metal fine particle thin film composed of metal fine particles such as gold attracts attention as a useful functional material. This metal fine particle thin film has useful physical properties in terms of optical properties, electrical properties, and catalytic properties. For example, by arranging regularly and three-dimensionally metal fine particles having a particle size of about the wavelength of light, It is known that a photonic crystal capable of controlling propagation and generation is formed. In addition, a phenomenon in which conductivity is changed in an arrayed nanometer-sized metal fine particle has been reported.

  The physical properties of the metal fine particle thin film described above generally depend on the structure such as the particle size, shape, and arrangement of the metal fine particles in the thin film. Therefore, it is required to precisely control the structure of the metal fine particles in the metal fine particle thin film. Table 1 lists conventional fine particle structure control methods (see, for example, Non-Patent Document 1). As shown in Table 1, a casting method in which metal fine particles are arranged in a self-organizing manner in the process of thinning, an ink jet method in which metal fine particles are ejected onto a substrate using an ejection nozzle, and the like are known as conventional techniques. Yes.

In addition, as another conventional technique, a method of producing a regular fine periodic structure of gold fine particles by mixing polystyrene beads with gold fine particles to form a thin film (see, for example, Non-Patent Document 2), on a substrate. There has been proposed a method in which gold fine particles are aggregated and fixed in a pattern by irradiating a solution containing gold fine particles applied to the film with electromagnetic waves through a mask pattern (see, for example, Non-Patent Document 3).
Masuda et al., “Material Integration”, 2001, Vol. 14, No. 8, p. 37-44 “Applied Spectroscopy”, 2002, Vol. 56, p. 1524-1530 “Nano Letters”, 2001, Volume 1, p. 365-369

  However, the above-described prior art performs the structure control of the metal fine particles at the time of forming the metal fine particle thin film, so that there is a problem that the structure control cannot be performed after the metal fine particle thin film is formed. Further, in the prior art, there is a problem that it is difficult to control the interval between the metal fine particles in the metal fine particle thin film with a nanometer size.

The present invention provides a method for producing a metal fine particle thin film capable of controlling the structure such as the particle size, shape, and arrangement of the metal fine particles with a nanometer size after the formation of the metal fine particle thin film, in view of the above-mentioned problems of the prior art. For the purpose.
It is another object of the present invention to provide a method for producing a metal fine particle thin film that can be patterned into the metal fine particle thin film by controlling the structure of the metal fine particle.

To solve this problem,
The invention according to claim 1 irradiates an electromagnetic wave capable of resonating with a local surface plasmon generated in a state in which the metal fine particles are close to each other on a thin film containing substantially spherical metal fine particles on the substrate. A method for controlling the structure of metal fine particles in a metal fine particle thin film , wherein the arrangement of the metal fine particles is changed.

The invention according to claim 2 is the method for controlling the structure of metal fine particles in the metal fine particle thin film according to claim 1, wherein the electromagnetic wave is irradiated as a beam.

The invention according to claim 3 is the method for controlling the structure of metal fine particles in the metal fine particle thin film according to claim 1 or 2, wherein electromagnetic waves are polarized.

The invention according to claim 4 is the metal particle structure control method in the metal particle thin film according to any one of claims 1 to 3, wherein either one or both of the electromagnetic wave beam and the substrate are moved. .

  According to the method for producing a metal fine particle thin film of the present invention, local surface plasmons generated on the surface of metal fine particles are excited by resonating with an irradiated electromagnetic wave, and then the energy is converted into lattice vibration energy of metal atoms. Relax. In addition, a metal atom in a charged state receives a Coulomb force by interacting with an electric field of an irradiated electromagnetic wave. Therefore, after the formation of the metal fine particle thin film, the movement of metal atoms can be activated and the structure of the metal fine particles such as the particle size, shape, and arrangement can be controlled.

  Further, according to the method for producing a metal fine particle thin film of the present invention, the structure of the metal fine particle in the metal fine particle thin film can be locally and selectively controlled by adjusting the irradiation diameter and polarization of the electromagnetic wave. Therefore, patterning by controlling the structure of the metal fine particles can be performed by scanning such an electromagnetic wave on the metal fine particle thin film.

One embodiment of a method for producing a metal fine particle thin film according to the present invention will be described below.
First, a uniform metal fine particle thin film is produced.
The metal fine particle thin film is a metal fine particle formed by aggregation of metal atoms on a substrate. The film thickness is 0.3 nm to 10 μm, and the particle diameter of the metal fine particles is 0.3 nm to 1 μm. In addition, as a kind of metal, Li, K, Rb, Ba, Sr, Ca, Na, Mg, Be, Al, U, Ti, Zr, Mn, Zn, Cr, Fe, C ⁺ , Co, Ni, Mo Sn, Pb, Cu, Cu ⁺ , Hg ₂ , Ag, Hg, Pd, Pt, and Au are used. These metals generate plasmons as described in the next paragraph.
A method for producing a uniform metal fine particle thin film is not particularly limited, and a known production method can be applied. For example, a spin coat method, a dip coat method, or the like is used. A commercially available metal fine particle thin film may also be used.

Next, the structure control of the metal fine particles in the metal fine particle thin film is performed.
As shown in FIG. 1, local surface plasmons 2 are generated in the metal fine particles 1 in the metal fine particle thin film. Plasmon is a quantum theory of free electrons (plasma oscillation) that vibrates in the metal. What is generated on the metal surface is generated on a local surface such as surface plasmon or metal fine particles 1. What it does is called local surface plasmon 2.

  The local surface plasmon 2 can resonate with the electromagnetic wave 3 having a specific frequency and absorb the light energy. This phenomenon is called local plasmon resonance. It is known that the absorption frequency of the local surface plasmon 2 generally varies depending on the structure such as the particle size, shape, and arrangement of the metal fine particles 1. Therefore, the absorption frequency is different between the case where the metal fine particles 1 are isolated as shown in FIG. 1A and the case where they are close to each other as shown in FIG.

  When local plasmon resonance occurs, the local surface plasmon 2 is excited and subsequently releases energy and relaxes. At this time, the released energy is transferred to the metal atom as lattice vibration (phonon) energy, and the vibration motion is activated. In addition, the metal atoms in the plasma state receive a Coulomb force by interacting with the electric field of the irradiated electromagnetic wave. Accordingly, the structure of the metal fine particles 1 such as the particle size, shape, and arrangement changes. For example, as shown in FIG. 2A, when the electromagnetic wave 3 is irradiated to the substantially spherical metal fine particles 1, the shape of the metal fine particles 1 becomes flat as shown in FIG. May be narrowed.

When the metal fine particle 1 is irradiated with the electromagnetic wave 3 having a frequency different from the absorption frequency of the local surface plasmon 2, the Coulomb interaction is mainly induced rather than the local plasmon resonance. Moreover, the radiation pressure of the electromagnetic wave 3 is also generated. Therefore, as shown in FIG. 3A, when such an electromagnetic wave 3 is irradiated to the metal fine particles 1, as shown in FIG. 3B, the particle diameter and shape of the metal fine particles 1 are not changed so much. The sequence can be changed mainly.
Note that when the structure of the metal fine particles 1 is changed by the irradiation of the electromagnetic wave 3, the absorption frequency of the local surface plasmon 2 is also changed. Therefore, if the electromagnetic wave 3 having a specific frequency is continuously irradiated, the local plasmon resonance is not induced after a predetermined time.

  By utilizing such a phenomenon, after the formation of the metal fine particle thin film, the structure of the metal fine particles in the metal fine particle thin film, such as the particle size, shape, and arrangement, can be controlled with a nanometer size. Therefore, physical properties such as optical characteristics, electrical characteristics, and catalytic characteristics of the metal fine particle thin film can be controlled.

  FIG. 4 shows an example of a fine particle thin film structure control apparatus suitable for the metal fine particle thin film manufacturing method of the present invention. The fine particle thin film structure control device of this example is schematically configured from an electromagnetic wave generator 10, a mounting device 20, and an observation device 30.

The electromagnetic wave generator 10 is an apparatus that generates an electromagnetic wave 3 for irradiating a metal fine particle thin film. The electromagnetic wave generator 10 is provided with an electromagnetic wave source 11 at the top. From this electromagnetic wave generation source 11, an electromagnetic wave 3 having an irradiation energy of 1 mW or more and a frequency of 10 ¹¹ to 10 ¹⁸ Hz is generated and irradiated downward.

A polarizing plate 12 is provided below the electromagnetic wave generation source 11. The electromagnetic wave 3 becomes linearly polarized light having a predetermined angle by the polarizing plate 12. This linearly polarized light has a property that local plasmon resonance is easily induced in the metal fine particles 1 arranged in parallel with the polarization direction of the electromagnetic wave 3. This property occurs because the distribution of the local surface plasmons 2 changes due to the alignment of the metal fine particles 1 in a straight line, and polarization characteristics are induced in the local plasmon resonance. Therefore, as shown in FIG. 5A, when the polarization direction of the electromagnetic wave 3 is adjusted using the polarizing plate 12 to irradiate the metal fine particles 1, the structure control of the metal fine particles 1 is performed as shown in FIG. 5B. Can be selectively performed.
In addition, when the structure control of the metal fine particles 1 in the metal fine particle thin film is performed non-selectively, a circularly polarized or non-polarized electromagnetic wave 3 is used.

Is convergent lens 1 3 is provided on the lower polarizing plate 1 2. Electromagnetic wave 3 is converged by the converging lens 1 3, a beam whose irradiation diameter is reduced to about half the wavelength of the electromagnetic wave 3 irradiated (diffraction limit). Therefore, the structure control of the metal fine particles 1 in the metal fine particle thin film can be locally performed.

  The placement device 20 is a place for placing a metal fine particle thin film, and includes a hot plate 21 and a movable stage 22 in contact with the lower portion thereof. The hot plate 21 is temperature-controllable, and the metal fine particle thin film is directly placed thereon. The movable stage 22 is for moving the hot plate 21 horizontally. By using the mounting device 20 having such a configuration, it is possible to irradiate the electromagnetic wave 3 generated from the electromagnetic wave generator 10 to an arbitrary place of the metal fine particle thin film at an arbitrary temperature. Therefore, the metal fine particle thin film can be patterned by controlling the structure of the metal fine particle 1.

The observation apparatus 30 is an apparatus for observing the shape of the metal fine particle thin film. In this observation device 30, a light source 31 is provided on the side of the electromagnetic wave irradiation device 10, and detection from the light source 31 of 10 mW or less used for any of Raman spectroscopy, infrared spectroscopy, and fluorescence spectroscopy. Light 32 is emitted toward the mounting device 20. The detection light 32 is converged by the converging lens 33 and is irradiated to the irradiation part of the electromagnetic wave 3 in the mounting device 20. Thereafter, the detection light 32 traveling below the mounting device 20 is collected by the condenser lens 34, and then separated by the spectroscope 35 for each frequency and then detected by the detector 36.
Therefore, by using the observation device 30, the structure of the metal fine particle thin film can be finely observed.

As an application example of the metal fine particle thin film produced by the method for producing a metal fine particle thin film of the present invention, there is a highly sensitive detection method of a compound by Raman spectroscopy.
Raman spectroscopy is an analysis method in which excitation light is incident on a compound to be measured and the vibration mode of the molecules of the compound is detected by detecting scattered light (Raman scattered light). Since this Raman scattered light undergoes a two-photon process involving the photon of the excitation light and the photon of the Raman scattered light, the light intensity is generally very small.

However, by fixing the compound to be measured to the metal fine particle thin film to generate Raman scattered light from the compound and inducing local plasmon resonance, the light intensity of the Raman scattered light can be increased up to 10 ¹⁵ times (photon / second). It is known that it can be enhanced. This phenomenon is called surface enhanced Raman scattering. Therefore, the structure of the metal fine particles 1 in the metal fine particle thin film is controlled by the method for producing the metal fine particle thin film of the present invention, and the absorption frequency of the local surface plasmon is adjusted so as to overlap with the frequency of the excitation light used in Raman spectroscopy. As a result, the surface-enhanced Raman effect can be optimized.

  Hereinafter, the present invention will be described in more detail by way of examples. The present invention is not limited to the following examples.

[Example 1]
In Example 1, a structure-controlled metal fine particle thin film was produced using the method for producing a metal fine particle thin film of the present invention. The specific procedure is shown below. In the production of the metal fine particle thin film, the fine particle thin film structure control apparatus was used.

First, a uniform metal fine particle thin film was produced.
As the metal fine particles 1, gold fine particles having a particle diameter of 20 nm were used, and a 0.01% by weight colloidal aqueous solution containing the gold fine particles was prepared. The colloidal aqueous solution was applied onto a glass substrate and dried at 4 ° C. to prepare a metal fine particle thin film. The film thickness was 20 nm (one layer). When this metal fine particle thin film was examined with an ultraviolet visible absorptiometer, a large peak appeared in the vicinity of 650 to 750 nm. This peak is due to local plasmon resonance of the gold fine particles.

Next, the structure of the metal fine particle thin film was controlled using local plasmon resonance.
The metal fine particle thin film was placed and fixed on the placement device 20 of the fine particle thin film structure control device. Subsequently, the electromagnetic wave irradiation device 10 was used to irradiate the metal fine particle thin film with the electromagnetic wave 3 capable of resonating with local surface plasmons. As the electromagnetic wave 3, a laser beam having a wavelength of 730 nm and an output of 50 mW was used. The irradiation time was 1 second. Moreover, the temperature of the hot plate 21 at the time of irradiation was 24 ° C. As the converging lens 13, a 50 × objective lens was used. Further, the polarization direction of the laser light was adjusted by the polarizing plate 12 so as to be parallel to the glass substrate.
FIG. 6 shows atomic force micrographs of the metal fine particle thin film before and after laser light irradiation. As is clear from these photographs, the shape of the gold fine particles in the metal fine particle thin film after the irradiation is changed from a spherical shape to a flat shape as compared with before the irradiation.

Further, it was confirmed that the structure of the gold fine particles did not change when the irradiation time of the laser beam was further extended for several seconds. This is because the absorption wavelength of the local surface plasmon is changed by changing the shape between the gold fine particles.
Furthermore, when the movable stage 22 of the mounting apparatus 20 was moved while irradiating the laser beam, as shown in FIG. 7, the structural change of the gold fine particles in the metal fine particle thin film was locally induced. Therefore, it became clear that the patterning by the structure control of the gold fine particles can be performed. Further, patterning was performed by irradiating the metal fine particle thin film while changing the irradiation output of the laser beam. As a result, it was confirmed that the line formed by patterning was faint at 10 mW and thick and blurred at 20 mW, but was satisfactorily drawn at 30 mW or more.

[Example 2]
In Example 2, the surface-enhanced Raman effect was measured using the metal fine particle thin film produced by the method for producing a metal fine particle thin film of the present invention. The specific procedure is shown below.

  As a compound to be measured, sodium glutamate was used. Using this sodium glutamate, an aqueous solution having a concentration of 1 μM was prepared, and this aqueous solution was applied to a gold fine particle thin film produced by the same production method as in Example 1 and dried to obtain a measurement sample. As the gold fine particle thin film, three types were used: one irradiated with a laser having a wavelength of 730 nm, one irradiated with a laser having a wavelength of 530 nm, and one not irradiated. The output at the time of irradiation with a laser with a wavelength of 730 nm and a laser with a wavelength of 530 nm was 50 mW and the irradiation time was 1 second. Using this measurement sample, Raman spectroscopic measurement was performed. In addition, the wavelength of the excitation light in the Raman spectroscopic measurement was 730 nm, and the output was 1 mW.

FIG. 8 shows a Raman spectrum obtained by measuring the measurement sample by Raman spectroscopy. (A) is a laser non-irradiation site | part, (b) is a laser irradiation site | part with a wavelength of 730 nm, (c) is a Raman spectrum in a laser irradiation site | part with a wavelength of 530 nm.
As a result, in the Raman spectrum of (b), peaks derived from the stretching vibration mode of the single bond between carbon atoms of sodium glutamate and the stretching vibration mode of the carboxyl group were detected. Therefore, it has been clarified that the surface-enhanced Raman effect can be effectively induced by controlling the structure of the metal fine particles 1 in the metal fine particle thin film with a laser having a wavelength of 730 nm.

  The method for producing a metal fine particle thin film of the present invention is useful as a method for controlling physical properties of a metal fine particle thin film, and can also be used as a highly sensitive detection method and information recording medium for other compounds.

It is a side view which shows the example of the metal microparticle and local surface plasmon in the metal microparticle thin film concerning embodiment of this invention. It is a side view which shows an example of the structure before and behind the local plasmon resonance of the metal microparticle in the metal microparticle thin film concerning embodiment of this invention. It is a side view which shows the other example of the structure before and behind the local plasmon resonance of the metal microparticle in the metal microparticle thin film concerning embodiment of this invention. It is a top view which shows an example of the structure before and behind the local plasmon resonance of the metal microparticle by the linearly polarized electromagnetic wave concerning embodiment of this invention. It is a figure which shows an example of the fine particle structure control apparatus used for the manufacturing method of the metal fine particle thin film concerning embodiment of this invention. 3 is an atomic force micrograph of a metal fine particle thin film in Example 1. FIG. 1 is an atomic force micrograph of a patterned metal fine particle thin film in Example 1. FIG. 6 is a diagram showing a Raman spectrum of a measurement sample in Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Metal fine particle, 2 ... Local surface plasmon, 3 ... Electromagnetic wave

Claims (4)

By irradiating a thin film containing substantially spherical metal fine particles on a substrate with electromagnetic waves capable of resonating with local surface plasmons generated when the metal fine particles are close to each other, the arrangement of the metal fine particles is changed. A method for controlling the structure of metal fine particles in a metal fine particle thin film. 2. The method for controlling the structure of metal fine particles in a metal fine particle thin film according to claim 1, wherein the electromagnetic wave is irradiated as a beam. 3. The method for controlling the structure of metal fine particles in a metal fine particle thin film according to claim 1 or 2, wherein electromagnetic waves are polarized . 4. The method of controlling a metal fine particle structure in a metal fine particle thin film according to claim 1, wherein either or both of the electromagnetic wave beam and the substrate are moved.

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