JP2012052848A - Scattering near-field optical probe and near-field optical microscope including the same - Google Patents
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本発明は、散乱型近接場光プローブ、散乱型近接場光プローブを備えた近接場光学顕微鏡に関し、特に近接場光を用いた分光装置等で用いる散乱型近接場光プローブおよびそのプローブを備えた近接場光学顕微鏡に関するものである。 The present invention relates to a scattering near-field optical probe and a near-field optical microscope including a scattering near-field optical probe, and more particularly to a scattering near-field optical probe used in a spectroscopic device using near-field light and the probe. The present invention relates to a near-field optical microscope.
従来の光学顕微鏡では光の波動性による回折限界のため、得られる空間分解能は使用する光の波長の半分程度の大きさに制限されていた。
しかしながら、近年のナノテクノロジーの進歩により、光の回折限界を超える空間分解能で物質の光学特性を評価する重要性が高まっている。
これらのニーズに応えるために、物質表面に局在する近接場光を利用した近接場光学顕微鏡が開発され、光の回折限界を超える空間分解能で物質の光学特性の評価が可能になった。
In the conventional optical microscope, the spatial resolution obtained is limited to about half the wavelength of the light used because of the diffraction limit due to the wave nature of the light.
However, recent advances in nanotechnology have increased the importance of evaluating the optical properties of materials with spatial resolution exceeding the diffraction limit of light.
In order to meet these needs, a near-field optical microscope using near-field light localized on the surface of the material has been developed, and the optical properties of the material can be evaluated with a spatial resolution exceeding the diffraction limit of light.
従来の近接場光学顕微鏡は大きく分けて開口型と散乱型（無開口型）に分類される。
開口型近接場光プローブを有する近接場光学顕微鏡では、先鋭化した光ファイバー先端に遮光性金属をコーティングして微小開口を設けたものをプローブとして用いる。光ファイバー末端からレーザーを入射すると開口部近傍に近接場光が発生する。
試料−プローブ間に働く原子間力やシェアフォースを利用してプローブを試料に接近させ、開口部近傍に発生した近接場光と試料の相互作用による散乱光や発光を検出する。
微小開口を通して光を試料に照射するため、開口の大きさ程度（〜１００ｎｍ）の空間分解能が得られるが、励起光として用いることができる光量は弱いため、信号光量が得易い蛍光分析などの測定に向いている。
Conventional near-field optical microscopes are roughly classified into an aperture type and a scattering type (no aperture type).
In a near-field optical microscope having an open-type near-field optical probe, a probe having a sharp opening formed by coating a light-shielding metal on a sharpened optical fiber tip is used as a probe. When a laser is incident from the end of the optical fiber, near-field light is generated near the opening.
Using the atomic force or shear force acting between the sample and the probe, the probe is brought close to the sample, and scattered light and luminescence due to the interaction between the near-field light generated near the opening and the sample are detected.
Since the sample is irradiated with light through the minute aperture, spatial resolution about the size of the aperture (up to 100 nm) can be obtained, but the amount of light that can be used as excitation light is weak, so measurement such as fluorescence analysis that easily obtains the signal light amount Suitable for.
一方、散乱型近接場光プローブを有する近接場光学顕微鏡では、金属のプローブに外部から光を照射し、プローブ先端で発生した近接場光と試料の相互作用による散乱光や発光を検出する。
この際、プローブ先端における金属の表面プラズモン共鳴を誘起することで、プローブ先端において局所的に著しく増強された電場が発生し、散乱光の強度を高めることができる。
そのため、信号光量の得難いラマン分光、非線形分光にも用いることができる。空間分解能はプローブの先端径程度（〜２０ｎｍ）となる。
散乱型の近接場光学顕微鏡においては、プローブ先端の金属の表面プラズモンを効率よく励起し、プローブ先端部における電場強度を高めることが、感度の高い分光測定を行う上で重要である。
そのためには、励起レーザー光の波長と金属プローブが持つプラズモン共鳴波長を一致させる必要がある。
また、表面プラズモン励起の効率は、非特許文献１で開示されているように金属の材質に大きく依存しており、可視光領域では純金属を利用した場合は銀が最も効率がよく、ついで金の効率がよい。
従来において、近接場光学顕微鏡用の金属プローブを作製する代表的な手段としては、カンチレバーに金属を蒸着またはめっきする方法（特許文献１）や、金属細線を電解研磨することにより作製する方法（非特許文献２）が知られている。
On the other hand, a near-field optical microscope having a scattering-type near-field light probe irradiates a metal probe with light from the outside, and detects scattered light and light emission due to the interaction between the near-field light generated at the probe tip and the sample.
At this time, by inducing metal surface plasmon resonance at the tip of the probe, an electric field remarkably enhanced locally is generated at the tip of the probe, and the intensity of scattered light can be increased.
Therefore, it can also be used for Raman spectroscopy and nonlinear spectroscopy where it is difficult to obtain a signal light amount. The spatial resolution is about the tip diameter of the probe (˜20 nm).
In a scattering-type near-field optical microscope, it is important for highly sensitive spectroscopic measurement to efficiently excite the metal surface plasmon at the tip of the probe and increase the electric field strength at the tip of the probe.
For this purpose, it is necessary to match the wavelength of the excitation laser light with the plasmon resonance wavelength of the metal probe.
In addition, the efficiency of surface plasmon excitation largely depends on the metal material as disclosed in Non-Patent
Conventionally, as a typical means for producing a metal probe for a near-field optical microscope, a method of depositing or plating a metal on a cantilever (Patent Document 1) or a method of producing a metal probe by electropolishing a metal thin wire (Non-Patent Document 1) Patent document 2) is known.
上記した散乱型近接場光プローブを備えた近接場光学顕微鏡によるラマン測定では、一部の試料においてレーザー光によって蛍光が発生する場合があり、微弱なラマン信号が蛍光に覆い隠されてしまうという課題を有している。
この場合、より長波長の励起光を使用することで蛍光を回避することができる。しかしながら、従来の手法で作製した金属プローブは図３（ａ）に示すように可視光域に単一のプラズモン共鳴ピークしかもたないため、試料の蛍光を回避することからより長波長の励起光を使用した場合において、電場増強を示さないという問題が生じる。
In the Raman measurement by the near-field optical microscope equipped with the above-described scattering-type near-field optical probe, there is a case where fluorescence is generated by laser light in some samples, and a weak Raman signal is covered by the fluorescence. have.
In this case, fluorescence can be avoided by using excitation light having a longer wavelength. However, since the metal probe produced by the conventional method has only a single plasmon resonance peak in the visible light region as shown in FIG. 3 (a), the excitation light having a longer wavelength is avoided in order to avoid fluorescence of the sample. When used, there is a problem of not showing an electric field enhancement.
本発明は、上記課題に鑑み、従来の散乱型近接場光プローブが電場増強を示す波長領域だけでなく、可視光の長波長領域においても電場増強を示す散乱型近接場光プローブおよび該散乱型近接場光プローブを備えた近接場光学顕微鏡の提供を目的とする。 In view of the above problems, the present invention provides a scattering near-field optical probe that exhibits an electric field enhancement not only in a wavelength region where a conventional scattering near-field optical probe exhibits an electric field enhancement, but also in a long wavelength region of visible light, and the scattering An object is to provide a near-field optical microscope equipped with a near-field optical probe.
本発明のプローブは、 プローブの先端部に光源からの光を照射し、プローブの先端部に近接場光を発生させる散乱型近接場光プローブであって、
前記プローブは、該プローブの先端部に、角をなす２辺が交わって形成された鋭角の頂点を有する平板状の金属単結晶を備え、
前記プローブの先端部に、前記鋭角の頂点を二等分する軸に対して平行な電界成分を有する光が光源から照射された際に、可視光の長波長領域においても電場増強を示すことを特徴とする。
また、本発明の近接場光学顕微鏡は、試料測定用のプローブと該プローブの先端部に外部より光を照射する光源とを備え、前記先端部に前記光源より光を照射することで発生する近接場光を用いて測定を行う近接場光学顕微鏡であって、
試料測定用のプローブが、上記した散乱型近接場光プローブによって構成されていることを特徴とする。
The probe of the present invention is a scattering near-field light probe that irradiates light from a light source to the tip of the probe and generates near-field light at the tip of the probe,
The probe comprises a flat metal single crystal having an acute apex formed by intersecting two sides forming an angle at the tip of the probe,
When the tip of the probe is irradiated from the light source with light having an electric field component parallel to the axis that bisects the acute vertex, the electric field is enhanced even in the long wavelength region of visible light. Features.
Further, the near-field optical microscope of the present invention includes a probe for measuring a sample and a light source that irradiates light from the outside to the tip of the probe, and the proximity generated by irradiating the tip from the light source A near-field optical microscope that performs measurement using field light,
The sample measurement probe is constituted by the above-described scattering-type near-field optical probe.
本発明によれば、従来の散乱型近接場光プローブが電場増強を示す波長領域だけでなく、可視光の長波長領域においても電場増強を示す散乱型近接場光プローブおよび該散乱型近接場光プローブを備えた近接場光学顕微鏡を実現することができる。 According to the present invention, the conventional scattered near-field light probe exhibits an electric field enhancement not only in the wavelength region where the electric field enhancement occurs, but also in the long wavelength region of visible light, and the scattered near-field light. A near-field optical microscope with a probe can be realized.
つぎに、本発明の実施形態における散乱型近接場光プローブおよび該散乱型近接場光プローブを備えた近接場光学顕微鏡の構成例について説明する。
本実施形態のプローブは、先端部に光源からの光を照射し、プローブの先端部に近接場光を発生させる散乱型近接場光プローブであって、該プローブの先端部に、角をなす２辺が交わって形成された鋭角の頂点を有する平板状の金属単結晶を備える。
以下に、平板状の金属単結晶の作製例について説明する。
まず、散乱型近接場光プローブの作製に際し、散乱型近接場光プローブに用いる平板状の金属単結晶を用意する。
金属としては金、銀、銅、白金、アルミニウム等が挙げられるが、この中では可視光域にプラズモン共鳴波長をもつ金、銀が好適である。ここでは、平板状の金属単結晶の材料として金が用いられる。
平板状の金単結晶の作製方法は特に限定されるものではないが、代表的な作製例として特開平５−２０１７９３号公報やＩｎｏｒｇａｎｉｃ Ｃｈｅｍｉｓｔｒｙ，４５，８０８（２００６）に開示されている方法を用いることができる。
特開平５−２０１７９３号公報には金錯体溶液から基板表面に金単結晶を析出させる方法が開示されている。
この例は、金のヨウ化物錯体等のハロゲン化物の溶液から基板表面に金単結晶を析出させるものであり、数μｍから数ｍｍの大きさの平板状の金単結晶を得ることができる。
この方法によって得られる単結晶は、基板面に対して結晶の（１１１）面が平行となる平板状の形状となる。
これらの単結晶を基板の上方から見た場合の形状は、若干の割合で不定形のものが存在するものの、正六角形もしくは正三角形となり、多くが正三角形となる。本実施形態の散乱型近接場光プローブとしては正三角形の金単結晶を使用するのが好適である。
Next, a configuration example of a scattering near-field optical probe and a near-field optical microscope provided with the scattering near-field optical probe in the embodiment of the present invention will be described.
The probe of this embodiment is a scattering near-field light probe that irradiates light from a light source to the tip portion and generates near-field light at the tip portion of the probe, and has an
Below, the preparation example of a flat metal single crystal is demonstrated.
First, when manufacturing the scattering near-field optical probe, a flat metal single crystal used for the scattering near-field optical probe is prepared.
Examples of the metal include gold, silver, copper, platinum, and aluminum. Among these, gold and silver having a plasmon resonance wavelength in the visible light region are preferable. Here, gold is used as the material of the flat metal single crystal.
A method for producing a flat gold single crystal is not particularly limited, but as a typical production example, a method disclosed in Japanese Patent Application Laid-Open No. 5-201793 and Inorganic Chemistry, 45, 808 (2006) is used. be able to.
Japanese Patent Application Laid-Open No. 5-201793 discloses a method for depositing a gold single crystal on a substrate surface from a gold complex solution.
In this example, a gold single crystal is deposited on the surface of a substrate from a halide solution such as a gold iodide complex, and a flat gold single crystal having a size of several μm to several mm can be obtained.
The single crystal obtained by this method has a flat plate shape in which the (111) plane of the crystal is parallel to the substrate surface.
When these single crystals are viewed from the upper side of the substrate, there are irregular shapes at a certain ratio, but they are regular hexagons or regular triangles, and many are regular triangles. As the scattering-type near-field optical probe of the present embodiment, it is preferable to use an equilateral triangular gold single crystal.
図１にこの正三角形の平板状の金単結晶の模式的な形状を示す。
図１（ａ）は結晶の（１１１）面方向から見た上面図、図１（ｂ）は側面図である。
図示したように、正三角形の頂点部分はその最先端まで結晶の低指数面で囲まれた形状となり、結晶の主面である（１１１）面に平行な面に沿った頂角は必ず６０°と鋭角になる。
また、単結晶であるため、その最先端まで金原子が規則正しく配列している。そのため、先端は曲率半径が小さく、さらに曲率半径のばらつきが小さい。
FIG. 1 shows a schematic shape of this equilateral triangular tabular gold single crystal.
1A is a top view of the crystal viewed from the (111) plane direction, and FIG. 1B is a side view.
As shown in the figure, the apex portion of the equilateral triangle has a shape surrounded by the low index plane of the crystal up to its forefront, and the apex angle along the plane parallel to the (111) plane which is the main surface of the crystal is always 60 °. And an acute angle.
Moreover, since it is a single crystal, gold atoms are regularly arranged up to the forefront. Therefore, the tip has a small radius of curvature, and the variation in the radius of curvature is small.
図２に、本実施形態の散乱型近接場光プローブおよびそのプローブを用いた近接場光学顕微鏡の模式図を示す。
本実施形態における近接場光学顕微鏡は、試料測定用のプローブとして上記した散乱型近接場光プローブを備え、該プローブの先端部に外部の光源から光を照射することで発生する近接場光を用いて測定を行うように構成されている。
ここでは試料表面側から励起光を入射する反射型の近接場光学顕微鏡を例示しているが、試料裏面から励起光を入射する透過型の配置でも本発明を適用できる。平板状の金単結晶１は頂角を試料表面に対向させる配置でチューニングフォーク２の先端に取り付けられ、散乱型近接場光プローブとして使用される。
平板状の金単結晶１はチューニングフォーク２の代わりにカンチレバーのチップ先端や先鋭化した光ファイバー先端に取り付けることも可能である。
試料表面側に配置した対物レンズ４により、散乱型近接場光プローブ先端に励起レーザー光５を照射すると、プローブ先端に近接場光が発生する。
プローブと試料表面に働くシェアフォースにより距離制御を行いながらプローブを試料表面に近接させる。このとき、プローブ先端で発生した近接場光と試料の相互作用による散乱光や発光が発生する。
これらの検出光６を励起に用いたものと同一の対物レンズ４により集光し、検出器（不図示）で検出する。
試料からの散乱光には励起光と同じ波長のレーリー散乱光の他、ラマン散乱光も発生する。
このとき、プローブ先端、つまり、平板状の金単結晶の先端において表面プラズモンを励起することで結晶端における電場強度を増大させることができ、結晶端直下の局在した領域からのラマン散乱光強度を増強させることができる。これにより、試料の局所的なラマン分光測定が可能になる。
FIG. 2 shows a schematic diagram of a scattering-type near-field optical probe of the present embodiment and a near-field optical microscope using the probe.
The near-field optical microscope in this embodiment includes the above-described scattering-type near-field light probe as a sample measurement probe, and uses near-field light generated by irradiating light from an external light source to the tip of the probe. Configured to perform measurement.
Here, a reflective near-field optical microscope in which excitation light is incident from the sample surface side is illustrated, but the present invention can also be applied to a transmissive arrangement in which excitation light is incident from the back surface of the sample. The flat gold
The flat gold
When the excitation laser light 5 is irradiated to the tip of the scattering near-field light probe by the objective lens 4 arranged on the sample surface side, near-field light is generated at the tip of the probe.
The probe is brought close to the sample surface while the distance is controlled by the shear force acting on the probe and the sample surface. At this time, scattered light and light emission are generated by the interaction between the near-field light generated at the probe tip and the sample.
These detection lights 6 are collected by the same objective lens 4 used for excitation and detected by a detector (not shown).
In addition to Rayleigh scattered light having the same wavelength as the excitation light, Raman scattered light is also generated in the scattered light from the sample.
At this time, the electric field intensity at the crystal edge can be increased by exciting the surface plasmon at the probe tip, that is, the tip of the flat gold single crystal, and the Raman scattered light intensity from the localized region directly under the crystal edge Can be strengthened. Thereby, local Raman spectroscopic measurement of a sample is attained.
図３に、プローブ先端に励起レーザー光を照射した場合のプローブ先端部付近における電場増強度を有限差分時間領域法（ＦＤＴＤ： Ｆｉｎｉｔｅ−Ｄｉｆｆｅｒｅｎｃｅ Ｔｉｍｅ Ｄｏｍａｉｎ）により計算した結果を示す。
図３（ａ）は一般的に用いられる円錐形の金プローブ（先端曲率２０ｎｍ）のＦＤＴＤ計算結果、図３（ｂ）は本実施形態で用いる正三角形の平板状の金単結晶（一辺１μｍ，厚さ１００ｎｍ）プローブのＦＤＴＤ計算結果である。
励起レーザー光の照射方向はプローブ軸に対し垂直な方向であり、グラフの横軸は入射光の波長、縦軸はプローブ直下５ｎｍ位置における電場増強度｜Ｅ／Ｅ0｜2を示している。電場増強度がピークとなる波長がプラズモン共鳴波長である。
円錐形の金プローブは５００ｎｍ付近に単一のプラズモン共鳴ピークしか持たないが、本実施形態のプローブは５５０〜６００ｎｍ付近だけでなく、可視光の長波長側の８００ｎｍ付近にもより大きなプラズモン共鳴ピークを持つことがわかる。つまり、近接場ラマン測定において試料が蛍光を発生する場合、蛍光を回避するために、より長波長の励起光を用いた場合、一般に用いられる円錐形の金プローブでは可視光の長波長側では電場増強を示さない。
これに対し、本実施形態の散乱型近接場光プローブでは可視光の長波長側においてもより大きな電場増強を示す。
FIG. 3 shows a result of calculating the electric field enhancement intensity in the vicinity of the probe tip when the probe tip is irradiated with the excitation laser beam by the finite difference time domain method (FDTD).
FIG. 3 (a) is a FDTD calculation result of a commonly used conical gold probe (tip curvature: 20 nm), and FIG. 3 (b) is an equilateral triangular flat gold single crystal (one side of 1 μm, (
The irradiation direction of the excitation laser light is a direction perpendicular to the probe axis, the horizontal axis of the graph indicates the wavelength of the incident light, and the vertical axis indicates the electric field enhancement intensity | E / E 0 | 2 at a position 5 nm directly below the probe. The wavelength at which the electric field enhancement peak is the plasmon resonance wavelength.
The conical gold probe has only a single plasmon resonance peak near 500 nm, but the probe of this embodiment has a larger plasmon resonance peak not only near 550 to 600 nm but also near 800 nm on the long wavelength side of visible light. You can see that In other words, when the sample emits fluorescence in near-field Raman measurement, in order to avoid fluorescence, when using a longer wavelength excitation light, a generally conical gold probe uses an electric field on the longer wavelength side of visible light. Does not show enhancement.
In contrast, the scattering-type near-field light probe of this embodiment shows a larger electric field enhancement even on the long wavelength side of visible light.
本実施形態における金の単結晶は、該金の単結晶厚さの一辺の長さに対する比が１０以上１００以下であることが望ましい。
ここで、図４に正三角形の平板状の金単結晶（一辺１μｍ，厚さ１００ｎｍ）プローブ先端における電場増強度の励起レーザー光の照射角度依存性についてＦＤＴＤ計算を行った結果を示す。
入射光はＸ−Ｚ面内でＺ軸に対してθの角度で変化させ、入射光の偏光はＸ−Ｚ面内で入射光と垂直な方向に振動する直線偏光とした。
グラフの横軸は入射光の波長、縦軸はプローブ直下５ｎｍ位置における電場増強度｜Ｅ／Ｅ0｜2を示している。
これによると、入射光がＺ軸に平行な場合（θ＝０°）にプローブ先端における電場増強度は最小になり、Ｚ軸に垂直な場合に電場増強度が最大になることがわかった。
つまり、入射光のＺ軸方向の電界成分が大きいほど平板状の金単結晶先端で発生する電場増強度が大きいことを示す。また、Ｘ−Ｙ面内で励起光の照射方向を変化させた場合、電場増強度に大きな差は見られなかった。
The gold single crystal in the present embodiment preferably has a ratio of the gold single crystal thickness to the length of one side of 10 to 100.
Here, FIG. 4 shows the result of FDTD calculation on the irradiation angle dependence of the electric field enhancement intensity at the probe tip of the equilateral triangular flat gold single crystal (
The incident light was changed at an angle θ with respect to the Z axis in the XZ plane, and the polarization of the incident light was linearly polarized light that oscillated in the direction perpendicular to the incident light in the XZ plane.
The horizontal axis of the graph indicates the wavelength of incident light, and the vertical axis indicates the electric field enhancement intensity | E / E 0 | 2 at a position 5 nm directly below the probe.
According to this, it was found that when the incident light is parallel to the Z axis (θ = 0 °), the electric field enhancement at the probe tip is minimized, and when the incident light is perpendicular to the Z axis, the electric field enhancement is maximized.
In other words, the larger the electric field component of the incident light in the Z-axis direction, the greater the electric field enhancement generated at the tip of the flat gold single crystal. Further, when the irradiation direction of the excitation light was changed in the XY plane, no significant difference was observed in the electric field enhancement intensity.
以上に説明したように、本実施形態の構成によれば、プローブの先端部に、前記光源から前記鋭角の頂点を二等分する軸に対して平行な電界成分を有する光が照射された際に、
従来の散乱型近接場光プローブが電場増強を示す波長領域だけでなく可視光の長波長領域においても電場増強を示す散乱型近接場光プローブが得られる。
そのため、試料からの蛍光を回避するために、より長波長の励起光を用いた場合でも電場増強を得ることができ、蛍光する試料に対しても近接場ラマン測定が可能になる。
また、結晶端をプローブとして使用するため、先端曲率半径のばらつきが小さく、形状の再現性も良いため、測定の再現性向上も期待できる。
As described above, according to the configuration of the present embodiment, when the tip of the probe is irradiated with light having an electric field component parallel to an axis that bisects the acute angle vertex from the light source. In addition,
A scattering-type near-field light probe that exhibits electric field enhancement not only in the wavelength region where the conventional scattering-type near-field light probe exhibits electric field enhancement but also in the long wavelength region of visible light can be obtained.
Therefore, in order to avoid fluorescence from the sample, an electric field enhancement can be obtained even when excitation light having a longer wavelength is used, and near-field Raman measurement can be performed even for a fluorescent sample.
Further, since the crystal edge is used as a probe, the variation in the radius of curvature of the tip is small and the shape reproducibility is good, so that the reproducibility of measurement can be expected to be improved.
以下に、本発明の実施例について説明するが、それらは一例であり本発明はこれらの実施例の構成に限定されるものではない。
［実施例１］
実施例１として、本発明を適用した平板状の金単結晶の構成例について説明する。
まず、本実施例で使用する平板状の金単結晶を作製した。
図５は、本実施例の平板状の金単結晶の作製に用いられる平板状の金単結晶作製装置の概略図である。
図５に示される石英製の反応容器９に、純水５００ｍｌ、ヨウ素１２ｇおよびヨウ化カリウム４０ｇを投入し、攪拌溶解させた。
さらに、粉末状の金２ｇを投入して攪拌溶解させ、金錯体溶液１０とした。
基板８としてチタンを蒸着したシリコン基板を用い、金錯体溶液１０中に基板８を浸漬させた。
Examples of the present invention will be described below, but they are only examples, and the present invention is not limited to the configurations of these examples.
[Example 1]
As Example 1, a configuration example of a flat gold single crystal to which the present invention is applied will be described.
First, a flat gold single crystal used in this example was produced.
FIG. 5 is a schematic view of a flat gold single crystal manufacturing apparatus used for manufacturing the flat gold single crystal of this example.
In a
Further, 2 g of powdered gold was added and dissolved by stirring to obtain a
A silicon substrate on which titanium was vapor-deposited was used as the
次いで、溶液加熱手段１２としてマントルヒーター、溶液温度計測器１１としてテフロン（登録商標）をコートした熱電対を用い、溶液温度をモニターして溶液温度が９０℃で一定になるように温度調節器１３で調節しながら加熱した。
上記反応はドラフト内で行い、基板８上に形成される平板状の金単結晶１４が所望の大きさになるように反応時間、ドラフト排気量を調節し、基板８上に数十〜数百μｍの大きさの平板状の金単結晶１４を得た。
平板状の金単結晶１４は水洗後、５分間酸素プラズマ処理をした後、窒素雰囲気下において３０分間３００℃で熱処理した。
このようにして得た平板状の金単結晶のＳＥＭ像を、図１（ｃ）に示す。ここでは一辺が約２００ｍｍの大きさの正三角形の平板状の金単結晶が得られた。
Next, a mantle heater is used as the solution heating means 12, and a thermocouple coated with Teflon (registered trademark) is used as the solution
The above reaction is performed in a draft, and the reaction time and the draft exhaust amount are adjusted so that the flat gold
The flat gold
An SEM image of the flat gold single crystal thus obtained is shown in FIG. Here, an equilateral triangular plate-shaped gold single crystal having a side of about 200 mm was obtained.
このようにして作製した平板状の金単結晶の電場増強効果を検証した。
図６の図中に示す平板状の金単結晶は一辺が約５μｍの正三角形の形状をしている。
この平板状の金単結晶上に１ｗｔ％のポリスチレン溶液をスピンコーティングして約１００ｎｍの膜厚のポリスチレン薄膜を形成させ、平板状の金単結晶の（１１１）面上と結晶先端部においてラマン測定を行った。
測定には励起波長７８０ｎｍのレーザー、１００×ＮＡ０．９の対物レンズを使用し、露光時間２０ｓ、積算回数３回の条件でラマンスペクトルを取得した。
入射光は平板状の金単結晶の（１１１）面に垂直な方向から入射し、入射光の偏光方向は結晶の頂角を二等分する軸と平行な方向とした。
ポリスチレンは１０００ｃｍ−１付近にベンゼン骨格振動の強いラマンピークが観測される。
平板状の金単結晶の（１１１）面上と結晶先端部で１０００ｃｍ−１におけるラマン強度を比較すると、結晶先端部においてポリスチレンのラマン強度が約７．４倍強くなっていることが示された。
このように、正三角形の平板状の金単結晶を散乱型近接場光プローブとして用いることで、平板状の金単結晶先端において電場増強効果を得ることができることが実証できた。
平板状の金単結晶プローブは顕微鏡下でマイクロマニュピレータを使いて平板状の金単結晶をエポキシによりチューニングフォーク先端に固定することにより作製できる。
The electric field enhancement effect of the flat gold single crystal thus produced was verified.
The flat gold single crystal shown in FIG. 6 has an equilateral triangle shape with a side of about 5 μm.
A 1 wt% polystyrene solution is spin-coated on this flat gold single crystal to form a polystyrene thin film having a thickness of about 100 nm, and Raman measurement is performed on the (111) plane of the flat gold single crystal and at the tip of the crystal. Went.
For the measurement, a laser having an excitation wavelength of 780 nm and an objective lens of 100 × NA 0.9 were used, and a Raman spectrum was obtained under the conditions of an exposure time of 20 s and an integration count of 3 times.
Incident light was incident from a direction perpendicular to the (111) plane of the flat gold single crystal, and the polarization direction of the incident light was parallel to the axis that bisects the apex angle of the crystal.
In polystyrene, a Raman peak with strong benzene skeleton vibration is observed in the vicinity of 1000 cm-1.
Comparing the Raman intensity at 1000 cm-1 on the (111) plane of the flat gold single crystal and the crystal tip, it was shown that the Raman intensity of polystyrene was about 7.4 times stronger at the crystal tip. .
Thus, it was demonstrated that the electric field enhancement effect can be obtained at the tip of the flat gold single crystal by using the equilateral triangular flat gold single crystal as the scattering near-field optical probe.
A flat gold single crystal probe can be prepared by fixing a flat gold single crystal to the tip of a tuning fork with epoxy using a micromanipulator under a microscope.
［実施例２］
実施例２として、一般的に用いられる円錐形の金プローブと、本発明の平板状の金単結晶プローブを用いて色素（Ｏｉｌ Ｂｌｕｅ Ｎ）を添加したポリスチレン薄膜の近接場ラマン測定を行った例について説明する。
まず、５１４ｎｍ励起で近接場ラマン測定を行った。この測定では、添加した色素から蛍光が発生するため、どちらのプローブを用いた場合においてもポリスチレン固有のラマンスペクトルは確認しづらい。
そこで、蛍光を回避するために励起光を７８０ｎｍに変更した。
一般的に用いられる円錐形金プローブを用いた近接場ラマン測定においては色素からの蛍光を抑えることはできたものの、図３（ａ）に示すように７８０ｎｍにおいては電場増強効果がほとんど得られない。そのため、ポリスチレン薄膜からのラマン信号は微弱である。
一方、本発明の平板状の金単結晶プローブを用いた近接場ラマン測定においては、色素からの蛍光を抑え、かつ図３（ｂ）に示すように電場増強効果も得られるため、ポリスチレン薄膜からのラマン信号をＳ／Ｎよく検出することが可能となる。
[Example 2]
Example 2 was a near-field Raman measurement of a polystyrene thin film to which a dye (Oil Blue N) was added using a commonly used conical gold probe and a flat gold single crystal probe of the present invention. Will be described.
First, near-field Raman measurement was performed with 514 nm excitation. In this measurement, fluorescence is generated from the added dye, so that it is difficult to confirm the Raman spectrum specific to polystyrene, regardless of which probe is used.
Therefore, in order to avoid fluorescence, the excitation light was changed to 780 nm.
In near-field Raman measurement using a commonly used conical gold probe, although fluorescence from the dye could be suppressed, as shown in FIG. 3 (a), almost no electric field enhancement effect was obtained at 780 nm. . Therefore, the Raman signal from the polystyrene thin film is weak.
On the other hand, in the near-field Raman measurement using the flat gold single crystal probe of the present invention, the fluorescence from the dye is suppressed and the electric field enhancement effect is also obtained as shown in FIG. Can be detected with good S / N.
［実施例３］
実施例３として、平板状の金単結晶の膜厚が電場増強度に与える影響についてＦＤＴＤ計算を行った例について説明する。
図７に、結晶を一辺１μｍの正三角形とし、膜厚を１０ｎｍ、２０ｎｍ、１００ｎｍと変えた時の、結晶先端における電場増強度をＦＤＴＤにより計算した結果を示す。
グラフの横軸は入射光の波長、縦軸はプローブ直下５ｎｍ位置における電場増強度｜Ｅ／Ｅ0｜2を示している。
これによると金単結晶の膜厚を薄くしていくと可視光の長波長側８００ｎｍ付近のプラズモン共鳴ピークが著しく増大することがわかった。
このように、可視光域の長波長側の励起光を用いて高感度な近接場ラマン分光を行う場合は、膜厚が薄い金単結晶を用いることが有利であることが示された。
[Example 3]
As Example 3, an example in which FDTD calculation is performed on the influence of the thickness of the flat gold single crystal on the electric field enhancement will be described.
FIG. 7 shows the results of calculating the electric field enhancement at the tip of the crystal by FDTD when the crystal is an equilateral triangle having a side of 1 μm and the film thickness is changed to 10 nm, 20 nm, and 100 nm.
The horizontal axis of the graph indicates the wavelength of incident light, and the vertical axis indicates the electric field enhancement intensity | E / E 0 | 2 at a position 5 nm directly below the probe.
According to this, it was found that as the thickness of the gold single crystal is reduced, the plasmon resonance peak near 800 nm on the long wavelength side of visible light is remarkably increased.
Thus, it has been shown that it is advantageous to use a gold single crystal with a small film thickness when performing high-sensitivity near-field Raman spectroscopy using excitation light on the long wavelength side in the visible light region.
１：平板状の金単結晶
２：チューニングフォーク
３：試料
４：対物レンズ
５：励起レーザー光
６：検出光（散乱光、発光）
７：ピエゾステージ
８：基板
９：反応容器
１０：金錯体溶液
１１：溶液温度計測器
１２：溶液加熱手段
１３：温度調節器
１４：平板状金単結晶
1: Flat gold single crystal 2: Tuning fork 3: Sample 4: Objective lens 5: Excitation laser beam 6: Detection light (scattered light, emission)
7: Piezo stage 8: Substrate 9: Reaction vessel 10: Gold complex solution 11: Solution temperature measuring device 12: Solution heating means 13: Temperature controller 14: Flat gold single crystal
Claims (5)
前記プローブは、該プローブの先端部に、角をなす２辺が交わって形成された鋭角の頂点を有する平板状の金属単結晶を備え、
前記プローブの先端部に、前記光源から前記鋭角の頂点を二等分する軸に対して平行な電界成分を有する光が照射された際に、可視光の長波長領域においても電場増強を示すことを特徴とする散乱型近接場光プローブ。 A scattering type near-field light probe that irradiates light from a light source to the tip of the probe and generates near-field light at the tip of the probe,
The probe comprises a flat metal single crystal having an acute apex formed by intersecting two sides forming an angle at the tip of the probe,
When the tip of the probe is irradiated with light having an electric field component parallel to an axis that bisects the acute angle vertex from the light source, the electric field is enhanced even in a long wavelength region of visible light. A scattering-type near-field optical probe characterized by
前記試料測定用のプローブが、請求項１から４のいずれか１項に記載の散乱型近接場光プローブによって構成されていることを特徴とする近接場光学顕微鏡。 A near-field optical microscope that performs measurement using near-field light generated at the tip of a probe by irradiating the tip of the probe for sample measurement with light from a light source,
5. The near-field optical microscope, wherein the sample measurement probe is constituted by the scattering near-field optical probe according to claim 1.
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