JP5098955B2 - Near-field optical probe - Google Patents
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本発明は、近接場分光分析において高い空間分解能を与えることが可能な近接場光プローブに関し、特に、散乱型の近接場光プローブに関する。 The present invention relates to a near-field optical probe capable of providing high spatial resolution in near-field spectroscopic analysis, and more particularly to a scattering-type near-field optical probe.
可視光、赤外光を使用する従来の顕微分光分析では、原理的に、分析に用いる光の波長より小さな領域の分光解析を行うことはできない。ところが、近接場分光分析では、プローブ先端に局在する近接場光を利用して分光分析を行うものであるため、分析に使用する光の波長に基づく測定限界を有さず、近接場光の発生範囲、例えば数百ナノメートル程度の微小領域に対して分光（赤外、ラマンおよび蛍光）分析を行うことができ、表面ナノ化学構造解析に対して有効な手段を提供する。しかしながら、近接場光を実材料分析に適用するために必要な基本技術が未だ確立されておらず、実用化に向けて多くの努力を有する。 In the conventional microspectroscopic analysis using visible light and infrared light, in principle, spectral analysis in a region smaller than the wavelength of light used for analysis cannot be performed. However, near-field spectroscopic analysis uses near-field light localized at the probe tip to perform spectroscopic analysis, so there is no measurement limit based on the wavelength of light used for analysis, and near-field light Spectroscopic (infrared, Raman, and fluorescence) analysis can be performed on a microscopic region having a generation range, for example, about several hundred nanometers, and provides an effective means for surface nanochemical structural analysis. However, the basic technology necessary for applying near-field light to actual material analysis has not yet been established, and many efforts are made toward practical use.
例えば、近接場分光分析における空間分解能は、理論的には近接場光を発生させるためのプローブの先端径程度であるが、現状ではその１０倍程度に留まり、近接場本来の分解能を発揮することができていない。 For example, the spatial resolution in near-field spectroscopic analysis is theoretically about the tip diameter of a probe for generating near-field light, but currently it is only about 10 times that of the probe, and the near-field original resolution is exhibited. Is not done.
図１２は、散乱型の近接場分光分析の原理を示す図である。１００は、例えば原子間力顕微鏡（ＡＦＭ）で使用される先端径が０．１μｍ程度のプローブを示す。このプローブ１００の先端に例えば赤外光１１０を照射すると、プローブ先端において、その径と同じ程度の範囲で近接場光１２０が発生する。この近接場光１２０が試料１３０の表面に入射して反射された反射光１４０を検出し分光分析することにより、試料１３０の微小領域における化学的な情報を得ることができる。 FIG. 12 is a diagram showing the principle of scattering-type near-field spectroscopy. Reference numeral 100 denotes a probe having a tip diameter of about 0.1 μm used in, for example, an atomic force microscope (AFM). When the tip of the probe 100 is irradiated with, for example, infrared light 110, the near-field light 120 is generated in the same range as the diameter of the probe tip. By detecting and spectroscopically analyzing the reflected light 140 that is reflected when the near-field light 120 is incident on the surface of the sample 130, chemical information in a minute region of the sample 130 can be obtained.
この場合、試料１３０の分析域、即ち空間分解能は、理論的にはプローブ先端の径１５０と同等程度となる。従って、先端径が０．１μｍ程度のＡＦＭプローブを使用した場合は、理論的には０．１μｍ程度の空間分解能を期待することが出来る。 In this case, the analysis region of the sample 130, that is, the spatial resolution, is theoretically approximately the same as the diameter 150 of the probe tip. Therefore, when an AFM probe having a tip diameter of about 0.1 μm is used, a spatial resolution of about 0.1 μm can be expected theoretically.
従って、高い空間分解能を有する近接場分光分析を行うためには、プローブ先端の径を出来るだけ小さくすること、即ち、プローブの先鋭化が試みられている。ところが実際は、この方法によって期待通りの空間分解能を得ることは難しく、プローブ径を５０ｎｍ程度としても空間分解能はその１０倍の５００ｎｍ程度にとどまり、近接場光本来の分解能を発揮することが出来ない。 Therefore, in order to perform near-field spectroscopic analysis with high spatial resolution, attempts have been made to make the probe tip diameter as small as possible, that is, to sharpen the probe. However, in reality, it is difficult to obtain the expected spatial resolution by this method, and even if the probe diameter is about 50 nm, the spatial resolution is about 10 times that of 500 nm, and the original resolution of near-field light cannot be exhibited.
散乱型近接場光プローブにおける空間分解能低下の原因を、プローブ先端に光を照射した場合に発生する反射光が試料表面を照射することに求め、このような反射を最小限に抑えることによって空間分解能を向上させる努力が行われている。例えば、特許文献１に記載の近接場光プローブでは、その先端部分に横溝、ナノホールあるいは渦巻状のナノグループを設けることによって、この部分で反射、散乱された赤外光が試料表面に達しないようにし、これによって分解能の改善を図っている。 The reason for the decrease in spatial resolution in the scattering near-field optical probe is that the reflected light generated when the probe tip is irradiated illuminates the sample surface, and the spatial resolution is minimized by minimizing such reflection. Efforts are being made to improve. For example, in the near-field optical probe described in Patent Document 1, by providing a lateral groove, nanohole, or spiral nanogroup at the tip, infrared light reflected and scattered by this portion does not reach the sample surface. Thus, the resolution is improved.
特許文献１に記載の構造を有する近接場光プローブでは、従来のプローブに比べて空間分解能の改善が見られるが、未だ、理論値に近い空間分解能を得ることができず、従って、一層の工夫が必要とされている。 Although the near-field optical probe having the structure described in Patent Document 1 shows an improvement in spatial resolution as compared with the conventional probe, it still cannot obtain a spatial resolution close to the theoretical value. Is needed.
本発明は、従来の近接場光プローブにおける上記のような問題点に鑑みてなされたものであり、近接場分光分析において理論値に近い高い空間分解能を得ることが可能な近接場光プローブを提供することをその課題とする。 The present invention has been made in view of the above problems in the conventional near-field optical probe, and provides a near-field optical probe capable of obtaining a high spatial resolution close to the theoretical value in near-field spectroscopic analysis. The task is to do.
上記課題を解決するために、本発明では、コア部と、前記コア部の先端外周に形成した金属コート層と、前記金属コート層に設けた縦溝とを備える近接場光プローブを提供する。 In order to solve the above problems, the present invention provides a near-field optical probe comprising a core part, a metal coat layer formed on the outer periphery of the tip of the core part, and a longitudinal groove provided in the metal coat layer.
前記縦溝は、分析波長の２００分の１から５０分の１の幅を有していても良い。また、前記縦溝の深さは溝幅の４分の１程度であっても良い。更に、前記縦溝は複数個形成されていても良い。 The longitudinal groove may have a width of 1/200 to 1/50 of the analysis wavelength. Further, the depth of the longitudinal groove may be about a quarter of the groove width. Furthermore, a plurality of the longitudinal grooves may be formed.
さらに、本発明では、前記縦溝の下端が、前記近接場光プローブの先端部の曲率半径をＲ、前記縦溝下端と前記近接場光プローブ先端との間の距離をＬとするとき、Ｌ≦２Ｒを満足する位置に来る様にした、近接場光プローブを提供する。 Further, in the present invention, when the lower end of the vertical groove is R, the radius of curvature of the tip of the near-field optical probe is R, and the distance between the lower end of the vertical groove and the tip of the near-field optical probe is L, Provided is a near-field optical probe which comes to a position satisfying ≦ 2R.
本発明の近接場光プローブによれば、プローブ先端に設けた縦溝によって分析光のＳ偏光成分による影響が抑制されるため、当該プローブを用いた近接場分光分析において、理論値に近い高い空間分解能を実現させることが出来る。また、近接場光プローブの先端部の曲率半径をＲ、前記縦溝下端と前記近接場光プローブ先端との間の距離をＬとするとき、Ｌ≦２Ｒとなるように縦溝の下端の位置を決定することによって、Ｐ偏光に起因する近接場領域が縮小するので、プローブ先端付近でＰ偏光に起因する近接場光がより集中して、感度の向上をもたらし、その結果、分解能が向上する。 According to the near-field optical probe of the present invention, since the influence of the S-polarized component of the analysis light is suppressed by the vertical groove provided at the probe tip, in the near-field spectroscopic analysis using the probe, a high space close to the theoretical value. Resolution can be realized. Further, when the radius of curvature of the tip of the near-field optical probe is R and the distance between the lower end of the longitudinal groove and the tip of the near-field optical probe is L, the position of the lower end of the longitudinal groove so that L ≦ 2R. Since the near-field region caused by P-polarized light is reduced, the near-field light caused by P-polarized light is more concentrated in the vicinity of the probe tip, resulting in improved sensitivity, and as a result, resolution is improved. .
以下に、本発明の実施形態を、図面を参照して説明する。なお、以下の図面において、同一の符号は同一又は類似の構成要素を示すので、重複した説明は行わない。 Embodiments of the present invention will be described below with reference to the drawings. Note that, in the following drawings, the same reference numerals indicate the same or similar components, and thus redundant description will not be given.
［第１の実施形態］
図１（ａ）は、本発明の第１の実施形態にかかる散乱型近接場光プローブ１の構成を示す部分正面図であり、図１（ｂ）はその中心部を紙面に平行に切った場合の断面図、図１（ｃ）は図１（ａ）のＸ−Ｘ線上断面図である。図１（ａ）〜（ｃ）に示す様に、プローブ１は基部２と先端部分３を有しており、先端部分３は例えばＳｉＯ２、Ｓｉ３Ｎ４、Ｓｉ、Ｇｅ等を材料とするコア部３ａと金属コート層３ｂとで構成されている。なお、先端部分３のコア部３ａは基部２の先端部分をフッ酸緩衝溶液等によって溶解し先鋭化して形成したもので有り、従って両者は本来一体のものである。金属コート層３ｂは、コア部３ａ上に金属（Ａｕ、Ａｇ等）を例えば５０〜５００ｎｍの厚さに真空蒸着して形成される。
[First Embodiment]
FIG. 1A is a partial front view showing the configuration of the scattering near-field optical probe 1 according to the first embodiment of the present invention, and FIG. FIG. 1C is a cross-sectional view taken along the line XX of FIG. As shown in FIGS. 1A to 1C, the probe 1 has a base 2 and a tip portion 3, and the tip portion 3 is made of, for example, SiO 2 , Si 3 N 4 , Si, Ge, or the like. It is comprised by the core part 3a and the metal coat layer 3b. The core portion 3a of the tip portion 3 is formed by dissolving and sharpening the tip portion of the base portion 2 with a hydrofluoric acid buffer solution or the like, and therefore both are originally integral. The metal coat layer 3b is formed by vacuum-depositing metal (Au, Ag, etc.) on the core portion 3a to a thickness of 50 to 500 nm, for example.
本実施形態のプローブ１は、この金属コート層３ｂに縦長の溝４を形成したことを特徴としている。図１（ａ）あるいは（ｃ）に示す様に、溝４はプローブの先端部分３に複数本、例えば４乃至８本が形成される。各溝４の幅は、分析波長の１／２００〜１／５０程度の範囲で選定される。波長が１０μｍの赤外光を用いた分析の場合は、従って、溝４の幅は５０〜２００ｎｍとなる。一般に、赤外分光では２．５〜２５μｍ領域の波長を解析するために、溝４の幅は１０〜５００ｎｍの範囲で選定される。溝４の深さは溝幅の１／４程度である。 The probe 1 of the present embodiment is characterized in that a longitudinal groove 4 is formed in the metal coat layer 3b. As shown in FIG. 1 (a) or (c), a plurality of grooves 4, for example, 4 to 8 grooves 4 are formed in the tip portion 3 of the probe. The width of each groove 4 is selected in the range of about 1/200 to 1/50 of the analysis wavelength. In the case of analysis using infrared light having a wavelength of 10 μm, therefore, the width of the groove 4 is 50 to 200 nm. Generally, in order to analyze wavelengths in the 2.5 to 25 μm region in infrared spectroscopy, the width of the groove 4 is selected in the range of 10 to 500 nm. The depth of the groove 4 is about 1/4 of the groove width.
次に、図１（ａ）〜（ｃ）に示す散乱型近接場光プローブ１の製造方法の一例を説明する。例えばＳｉＯ２のロッドを引っ張りながら炭酸ガスレーザを照射して先端部分を切り離す。切り離した先端部分をフッ酸緩衝溶液により溶解し、先鋭化してプローブの先端部分３（コア部３ａ）を形成する。次に、この先端部分３にＡｕ等の真空蒸着を行い、金属コート層３ｂを形成する。 Next, an example of a method for manufacturing the scattering near-field optical probe 1 shown in FIGS. For example, the carbon dioxide laser is irradiated while pulling the SiO 2 rod to cut off the tip portion. The separated tip portion is dissolved with a hydrofluoric acid buffer solution and sharpened to form the tip portion 3 (core portion 3a) of the probe. Next, vacuum deposition of Au or the like is performed on the tip portion 3 to form a metal coat layer 3b.
このようにして、プローブ１の先端部分３が形成されると、次に、この部分を固定した後、Ａｒ、Ｇａ等のイオンビームを用いて金属コート層３ｂを掘り込み、溝４を形成する。先端部分３の固定方向を変え、イオンビーム加工を繰り返すことにより、所望の本数の溝４を先端部分３に形成する。 When the tip portion 3 of the probe 1 is formed in this way, next, after fixing this portion, the metal coat layer 3b is dug using an ion beam of Ar, Ga, etc., and the groove 4 is formed. . A desired number of grooves 4 are formed in the tip portion 3 by changing the fixing direction of the tip portion 3 and repeating ion beam processing.
以上のように、本発明の第１の実施形態にかかる散乱型近接場光プローブは、プローブの先端部分において複数の縦方向の溝を有しており、その溝の幅は分析波長の１／２００〜１／５０程度とされる。 As described above, the scattering near-field optical probe according to the first embodiment of the present invention has a plurality of vertical grooves at the tip portion of the probe, and the width of the grooves is 1 / (1) of the analysis wavelength. It is about 200 to 1/50.
図２および図３は、本発明の第１の実施形態にかかる近接場光プローブの効果を示す図である。図２は、従来の近接場光プローブを用いて行った赤外分光分析結果を可視化した画像Ａと本発明の第１の実施形態にかかる近接場光プローブを用いた場合の同様の画像Ｂを示す。両画像とも、分析によって得られた試料中のＳｉ−Ｏ分布を可視化している。また、何れの分光分析も先端径（Φ）が５００ｎｍの近接場光プローブを使用したが、本実施形態のプローブは図１（ａ）〜（ｃ）に示す縦溝を備え、従来のプローブはこのような縦溝を有していない（未加工）点で相違している。 2 and 3 are views showing the effect of the near-field optical probe according to the first embodiment of the present invention. FIG. 2 shows an image A obtained by visualizing the result of infrared spectroscopic analysis performed using a conventional near-field optical probe and a similar image B obtained using the near-field optical probe according to the first embodiment of the present invention. Show. Both images visualize the Si—O distribution in the sample obtained by analysis. Moreover, although the spectroscopic analysis used a near-field optical probe having a tip diameter (Φ) of 500 nm, the probe of this embodiment includes vertical grooves shown in FIGS. It is different in that it does not have such vertical grooves (unprocessed).
分析に用いた試料は、ＳｉＯ２膜領内に微小な樹脂（ＰＭＭＡ）領域を有している。画像Ａの分析によって、従来（縦溝の未加工のもの）のプローブによる空間分解能は１．５μｍであり、一方、画像Ｂの分析により、本実施形態のプローブによる空間分解能は０．７μｍであることが分かった。 The sample used for the analysis has a minute resin (PMMA) region in the SiO 2 film region. According to the analysis of the image A, the spatial resolution by the conventional probe (unprocessed flutes) is 1.5 μm, while, by the analysis of the image B, the spatial resolution by the probe of the present embodiment is 0.7 μm. I understood that.
図３は、プローブの縦溝の幅と空間分解能の関係を示すグラフである。図３のグラフ中、点Ａ、Ｂは、図２の画像Ａ、Ｂを測定したプローブに対応する。この実験ではプローブの先端径Φを５００ｎｍとしているので、理論分解能は５００ｎｍ（０．５μｍ）である。ところが、未加工のプローブでは、点Ａを含めてその空間分解能は理論値よりもかなり低い。これに対して、画像Ｂを得た測定実験では幅が０．１μｍの縦溝を形成したプローブを使用することにより、０．７μｍの分解能を得ている。この値は先端径の１．４倍である。従って、縦溝を形成した、先端径Φが０．０５μｍのプローブを用いた場合、０．１μｍの空間分解能を期待することが出来る。 FIG. 3 is a graph showing the relationship between the vertical groove width of the probe and the spatial resolution. In the graph of FIG. 3, points A and B correspond to the probe that measured the images A and B of FIG. In this experiment, since the tip diameter Φ of the probe is 500 nm, the theoretical resolution is 500 nm (0.5 μm). However, in the raw probe, the spatial resolution including the point A is considerably lower than the theoretical value. On the other hand, in the measurement experiment for obtaining the image B, a resolution of 0.7 μm is obtained by using a probe in which a longitudinal groove having a width of 0.1 μm is formed. This value is 1.4 times the tip diameter. Therefore, when a probe having a longitudinal groove and having a tip diameter Φ of 0.05 μm is used, a spatial resolution of 0.1 μm can be expected.
本発明の近接場光プローブによって空間分解能が向上する理由は、次のようなものであると考えられる。 The reason why the spatial resolution is improved by the near-field optical probe of the present invention is considered as follows.
図４は、ＦＤＴＤ（時間領域有限差分法）電磁界シミュレータを用いた近接場シミュレーションの結果を示す図である。図４のＣ、Ｄとも、先端径Φが０．５μｍでかつＡｕをコートしたプローブを用いており、検出光の波長は１０μｍである。一方、図Ｃの場合は、検出光としてＰ偏光を用い、図Ｄの場合はＳ偏光を用いた。図４Ｃより、Ｐ偏光をプローブの先端に照射した場合、入射光によって発生する強電界、即ち近接場はプローブの先端に集中していることが分かる。一方、図Ｄより、Ｓ偏光によって発生する近接場はプローブの側面に大きく広がっていることが分かる。このことから、Ｓ偏光に起因する近接場の場合、プローブ先端径の実効値が大きくなり、その結果、空間分解能を低下させているものと思われる。 FIG. 4 is a diagram illustrating a result of near-field simulation using an FDTD (time domain finite difference method) electromagnetic field simulator. Each of C and D in FIG. 4 uses a probe having a tip diameter Φ of 0.5 μm and coated with Au, and the wavelength of detection light is 10 μm. On the other hand, in the case of FIG. C, P polarized light was used as detection light, and in the case of FIG. D, S polarized light was used. FIG. 4C shows that when P-polarized light is applied to the tip of the probe, a strong electric field generated by incident light, that is, a near field is concentrated on the tip of the probe. On the other hand, it can be seen from FIG. D that the near field generated by the S-polarized light greatly spreads on the side surface of the probe. From this, in the case of the near field due to the S-polarized light, the effective value of the probe tip diameter increases, and as a result, it seems that the spatial resolution is lowered.
従って、検出光中に存在するＳ偏光成分を除去できれば、空間分解能が向上するものと考えられる。検出光中のＳ偏光成分を除去するために偏光フィルタを用いることが考えられるが、本発明者等の実験によれば、偏光フィルタの使用によって検出光の強度が低下し、試料による吸光度が大幅に低下する。その結果、分析の精度も低下するので、偏光フィルタの使用は好ましくない。 Therefore, it is considered that the spatial resolution can be improved if the S-polarized component present in the detection light can be removed. Although it is conceivable to use a polarizing filter in order to remove the S-polarized light component in the detection light, according to the experiments by the present inventors, the intensity of the detection light is reduced by the use of the polarizing filter, and the absorbance by the sample is greatly increased. To drop. As a result, the accuracy of the analysis also decreases, so the use of a polarizing filter is not preferable.
一方、本発明のプローブでは、プローブ先端に縦溝を設けることでＳ偏光による反射光を低減させることができるので、吸光度を低下させること無く、近接場分光分析における空間分解能を向上させることが出来る。 On the other hand, in the probe of the present invention, since the light reflected by S-polarized light can be reduced by providing a longitudinal groove at the probe tip, the spatial resolution in near-field spectroscopic analysis can be improved without reducing the absorbance. .
図５および図６に、本発明との比較のために、先端に縦溝に代わって横溝を設けたプローブにおける実験結果を示す。図５は、プローブ先端部分３０に複数の横溝３１を設けた近接場光プローブ２０を示す。この構造は、特許文献１に記載のプローブと基本的に同じ構造である。 5 and 6 show experimental results in a probe in which a lateral groove is provided instead of a longitudinal groove at the tip for comparison with the present invention. FIG. 5 shows the near-field optical probe 20 in which a plurality of lateral grooves 31 are provided in the probe tip portion 30. This structure is basically the same structure as the probe described in Patent Document 1.
図６は、図５の構造のプローブ２０に対して波長１０μｍの赤外線を照射して近接場光を発生させた場合の、空間分解能と横溝幅との関係を示すグラフである。プローブ２０の先端径Φは５００ｎｍである。この図から明らかなように、プローブ先端部分３０に横溝を形成しない（未加工の）プローブの場合に比べて、幅が０．５μｍの横溝を形成したプローブでは空間分解能がわずかに向上しているが、本発明の第１の実施形態にかかるプローブ１に比べるとその向上の割合は小さい。 FIG. 6 is a graph showing the relationship between spatial resolution and lateral groove width when near-field light is generated by irradiating the probe 20 having the structure of FIG. 5 with infrared light having a wavelength of 10 μm. The tip diameter Φ of the probe 20 is 500 nm. As is clear from this figure, the spatial resolution is slightly improved in the probe in which the lateral groove having a width of 0.5 μm is formed, compared with the case of the probe not forming the lateral groove in the probe tip portion 30 (unprocessed). However, the improvement rate is small compared to the probe 1 according to the first embodiment of the present invention.
［第２の実施形態］
上記第１の実施形態にかかる近接場光プローブ１は、プローブに縦溝加工を行うことにより、Ｓ偏光に起因するノイズを除去して分解能の向上を図っている。一方、近接場シミュレーションによると、Ｐ偏光に起因する近接場光の電界強度は、Ｓ偏光に起因する近接場光の電界強度に比べて遥かに大きい。従って、Ｐ偏光の影響を考慮することによって、更なる分解能の向上が期待される。
[Second Embodiment]
The near-field optical probe 1 according to the first embodiment is designed to improve resolution by removing noise caused by S-polarized light by performing longitudinal groove processing on the probe. On the other hand, according to near-field simulation, the electric field strength of near-field light caused by P-polarized light is much larger than the electric field strength of near-field light caused by S-polarized light. Therefore, further improvement in resolution is expected by considering the influence of P-polarized light.
図７に、近接場シミュレーションに基づく、Ｐ偏光に起因する近接場光の電界強度分布を示し、図８にＳ偏光に起因する近接場光の電界強度分布を示す。図７および図８において、図の（ａ）は電界強度分布のイメージ図、図（ｂ）は近接場光の１次元電界強度とプローブ先端からの距離との関係を示すグラフである。図７（ｂ）および図８（ｂ）の縦軸は電界強度を［（Ｖ／ｍ）２］で示し、横軸はプローブの先端（下端）直下を０とした場合のｘ軸方向の距離を示している。 FIG. 7 shows a field intensity distribution of near-field light caused by P-polarized light based on near-field simulation, and FIG. 8 shows a field intensity distribution of near-field light caused by S-polarized light. 7 and 8, (a) is an image diagram of electric field intensity distribution, and (b) is a graph showing the relationship between the one-dimensional electric field intensity of near-field light and the distance from the probe tip. 7 (b) and 8 (b), the vertical axis indicates the electric field strength as [(V / m) 2 ], and the horizontal axis indicates the distance in the x-axis direction when the position immediately below the tip (lower end) of the probe is 0. Is shown.
図７（ｂ）と図８（ｂ）のグラフを比較することによって明らかなように、Ｐ偏光に起因する近接場光の電界強度はＳ偏光に起因する近接場光の電界強度よりも遥かに大きい。また、Ｓ偏光に起因する近接場光の電界強度は、プローブ先端直下（ｘ＝０）からの距離によってあまり大きく変化しないが、Ｐ偏光に起因する近接場光の電界強度は、プローブ先端直下付近で強く、プローブ先端直下からの距離が大きくなるに伴って急激に減少する。従って、Ｐ偏光起因の近接場光発生領域をより小さくすることによって、プローブ先端付近にＰ偏光を集中させ、結果的にプローブに照射される光強度を大きくすることができる。 As is clear by comparing the graphs of FIG. 7B and FIG. 8B, the electric field strength of the near-field light caused by the P-polarized light is much larger than the electric field strength of the near-field light caused by the S-polarized light. large. In addition, the electric field strength of near-field light due to S-polarized light does not change so much depending on the distance from immediately below the probe tip (x = 0). It decreases strongly as the distance from directly below the probe tip increases. Therefore, by reducing the near-field light generation region caused by the P-polarized light, the P-polarized light can be concentrated near the tip of the probe, and as a result, the light intensity irradiated to the probe can be increased.
このような観点から、上記第１の実施形態にかかる近接場光プローブの縦溝の形状についてさらに検討を加えたところ、以下に示すような第２の実施形態にかかる近接場光プローブの形状を得ることができた。 From this point of view, when the shape of the longitudinal groove of the near-field optical probe according to the first embodiment is further studied, the shape of the near-field optical probe according to the second embodiment as described below is as follows. I was able to get it.
図９は、本発明の第２の実施形態にかかる近接場光プローブ１０の正面図である。このプローブ１０は、基本的に図１に示すプローブ１と同じ構造を有しているが、縦溝４’の下端４ａとプローブ先端１０ａまでの距離Ｌを、プローブ１０の先端１０ａの曲率半径Ｒに対して、
距離Ｌ≦２Ｒ （１）
となるようにしたことを特徴としている。
FIG. 9 is a front view of the near-field optical probe 10 according to the second embodiment of the present invention. This probe 10 basically has the same structure as the probe 1 shown in FIG. 1, but the distance L between the lower end 4a of the longitudinal groove 4 'and the probe tip 10a is set to the radius of curvature R of the tip 10a of the probe 10. Against
Distance L ≦ 2R (1)
It is characterized by having become.
即ち、縦溝４’を、その下端４ａとプローブ先端１０ａとの距離Ｌが、２Ｒ以下となるように、プローブ先端１０ａに接近（Ｌ≦２Ｒ）して形成する。縦溝４’の長さは、集光ビーム光のプローブ先端部３ａ付近でのビーム径以上の大きさが必要である。言い換えると、縦溝４’の上端は、ビーム光の焦点近傍を含むように形成される。縦溝４’の溝幅は、第１の実施形態の場合と同様に、分析波長の１／２００〜１／５０（赤外分析の場合、１０〜５００ｎｍ）であり、溝数は１本以上とされる。また、近接場光プローブ１０の先端径（曲率半径×２）は３μｍ以下とする。 That is, the vertical groove 4 ′ is formed close to the probe tip 10 a (L ≦ 2R) so that the distance L between the lower end 4 a and the probe tip 10 a is 2R or less. The length of the vertical groove 4 ′ needs to be larger than the beam diameter in the vicinity of the probe tip 3 a of the condensed beam light. In other words, the upper end of the vertical groove 4 ′ is formed so as to include the vicinity of the focal point of the beam light. The groove width of the longitudinal groove 4 ′ is 1/200 to 1/50 of the analysis wavelength (10 to 500 nm in the case of infrared analysis) as in the first embodiment, and the number of grooves is one or more. It is said. The tip diameter (curvature radius × 2) of the near-field optical probe 10 is 3 μm or less.
図９に示す近接場光プローブ１０は、縦溝４’が上記のような構造上の規定を有している他は、図１のプローブ１と同様の方法で作成される。 The near-field optical probe 10 shown in FIG. 9 is produced by the same method as that of the probe 1 of FIG. 1 except that the longitudinal groove 4 ′ has the above-mentioned structural definition.
図１０は、第２の実施形態にかかる近接場光プローブの効果を示す図であって、近接場光プローブの溝なしモデル、短い溝を有するモデル、および第２の実施形態にかかるモデルについて、それぞれのＦＤＴＤシミュレーション結果（図１０の（Ａ）〜（Ｃ））を示す。計算のモデルは、プローブ先端径５００ｎｍ、縦溝の幅２００ｎｍ、深さ１００ｎｍ、溝数４本とし、プローブはＳｉＯ２のプローブに厚さ１００ｎｍのＡｕ膜をコーティングして形成したものを用いた。また、近接場光生成のための入射光は、波長１０μｍのＰ偏光とした。この場合、プローブ先端部付近でのビーム径は約２０μｍとなる。 FIG. 10 is a diagram illustrating the effect of the near-field optical probe according to the second embodiment. The near-field optical probe has no groove model, a model having a short groove, and the model according to the second embodiment. The respective FDTD simulation results ((A) to (C) in FIG. 10) are shown. The calculation model was a probe tip diameter of 500 nm, a longitudinal groove width of 200 nm, a depth of 100 nm, and a number of grooves of 4. The probe was formed by coating a SiO 2 probe with a 100 nm thick Au film. The incident light for generating near-field light was P-polarized light having a wavelength of 10 μm. In this case, the beam diameter near the probe tip is about 20 μm.
図１０の（ａ）は溝なしモデルのプローブを示し、そのプローブでのＰ偏光に起因する近接場光電界強度分布のシミュレーション結果を図（Ａ）に示す。図１０の（ｂ）では、縦溝の下端がＬ＞２Ｒの位置にある、短い溝有りモデルのプローブを示し、図（Ａ）と同様のシミュレーション結果を図（Ｂ）に示す。さらに、図１０の（ｃ）では、縦溝の下端がＬ≦２Ｒの位置にある、長い溝有りモデルのプローブを示し、そのシミュレーション結果を図（Ｃ）に示す。図（Ａ）〜（Ｃ）のシミュレーション結果を比較することによって、長い溝有りモデルのプローブで、近接場領域が最も縮小していることが理解されるが、さらにこの効果は、各モデルでの先端直下５０ｎｍにおける近接場光の１次元電界強度分布を示す図１１を参照することによって、より明瞭となる。 FIG. 10A shows a probe of a grooveless model, and FIG. 10A shows a simulation result of a near-field light electric field intensity distribution caused by P-polarized light with the probe. FIG. 10B shows a probe with a short groove model in which the lower end of the vertical groove is at a position of L> 2R, and the simulation result similar to FIG. Further, FIG. 10C shows a long grooved probe in which the lower end of the longitudinal groove is located at L ≦ 2R, and the simulation result is shown in FIG. By comparing the simulation results of FIGS. (A) to (C), it can be understood that the near-field region is the most reduced in the long grooved probe. It becomes clearer by referring to FIG. 11 showing the one-dimensional electric field intensity distribution of near-field light at 50 nm immediately below the tip.
以上のように、縦溝４’の下端の位置が上記式（１）を満足するように、プローブに縦溝を形成することにより、近接場光の生成に使用する光ビーム中のＰ偏光成分がプローブ先端付近でより集中し、その結果、感度が向上し、Ｓ／Ｎ比が改善されて分解能がより向上する。 As described above, by forming the vertical groove in the probe so that the position of the lower end of the vertical groove 4 ′ satisfies the above formula (1), the P-polarized light component in the light beam used for generating the near-field light Are more concentrated in the vicinity of the probe tip. As a result, the sensitivity is improved, the S / N ratio is improved, and the resolution is further improved.
１、１０ 散乱型近接場光プローブ
２ プローブ基部
３ プローブ先端部分
３ａ コア部
３ｂ 金属コート層
４、４’ 縦溝
４ａ 縦溝下端
１０ａ プローブ先端（下端）
DESCRIPTION OF SYMBOLS 1, 10 Scattering type near-field light probe 2 Probe base part 3 Probe tip part 3a Core part 3b Metal coating layer 4, 4 'Vertical groove 4a Vertical groove lower end 10a Probe front end (lower end)
Claims (5)
コア部と、
前記コア部の先端外周に形成した金属コート層と、
前記金属コート層に設けた縦溝と、を備え、前記縦溝は前記外部光の波長の２００分の１から５０分の１の幅を有する、近接場光プローブ。 In a near-field optical probe for scattering-type near-field spectroscopic analysis in which analysis is performed using near-field light generated by external light irradiated to the probe tip,
The core,
A metal coat layer formed on the outer periphery of the core portion;
And a longitudinal groove provided in the metal coat layer , wherein the longitudinal groove has a width of 1/200 to 1/50 of the wavelength of the external light .
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