WO2019165715A1 - 一种基于等离激元纳米钉结构的多功能近场光学探针 - Google Patents

一种基于等离激元纳米钉结构的多功能近场光学探针 Download PDF

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WO2019165715A1
WO2019165715A1 PCT/CN2018/088740 CN2018088740W WO2019165715A1 WO 2019165715 A1 WO2019165715 A1 WO 2019165715A1 CN 2018088740 W CN2018088740 W CN 2018088740W WO 2019165715 A1 WO2019165715 A1 WO 2019165715A1
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tip
nano
nail
fiber
field optical
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PCT/CN2018/088740
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English (en)
French (fr)
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张晓阳
张彤
周桓立
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东南大学
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
    • G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
    • G01Q60/18—SNOM [Scanning Near-Field Optical Microscopy] or apparatus therefor, e.g. SNOM probes
    • G01Q60/22—Probes, their manufacture, or their related instrumentation, e.g. holders
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
    • G01Q70/00—General aspects of SPM probes, their manufacture or their related instrumentation, insofar as they are not specially adapted to a single SPM technique covered by group G01Q60/00
    • G01Q70/08—Probe characteristics
    • G01Q70/10—Shape or taper
    • G01Q70/12—Nanotube tips

Definitions

  • the invention relates to the field of near-field microscopic imaging, the field of waveguides and the field of nano-materials, in particular to a multifunctional near-field optical probe based on a plasmonic nano-nail structure.
  • Ultra-high resolution microscopic characterization is an important tool for studying microscopic nanostructures.
  • the traditional microscopic method of using optical lenses to form images is limited by the diffraction limit, and the resolution cannot exceed the wavelength level, which seriously restricts the development of nanotechnology.
  • electron microscopes have made significant breakthroughs in resolution, but they still have many drawbacks, such as: samples generally have good conductivity, and can not be used for insulator samples and solution samples; The vacuum environment; high-resolution imaging mode must use a high-voltage electron beam, which is highly destructive to the sample. Therefore, there is no special demand for samples and environment, and non-contact, non-destructive detection of near-field optical microscopy technology is increasingly favored by people.
  • the resolution of near-field optical microscopy is closely related to the topology and material properties of near-field probes.
  • the light beam passing through the probe must be limited as much as possible in the lateral direction; on the other hand, the luminous flux passing through the restricted area should be as large as possible to obtain a high letter. Noise ratio.
  • a non-porous probe is a probe that has no opening at the tip of the probe. Therefore, the inherent defects of the fiber probe can be avoided.
  • the tip of the needle can be thought of as one or several dipoles that interact with the surface of the sample, resulting in ultra-high optical confinement and local field enhancement.
  • its resolution is affected by the geometry of the tip, which can break through the bottleneck of 10nm, so the non-porous probe has great potential in improving spatial resolution.
  • the existing non-porous needle tips are mostly isotropic spherical, the resonance enhancement spectrum peak width, and the local effect of the light field is limited, so the obtained light intensity signal is weak, which affects the contrast of the detected image. Therefore, how to overcome the limitations of the above two types of probes, and improve the sensitivity of the detection signal while improving the resolution is a key technical problem to be solved in the field of near-field probes and even optical microscopes.
  • the composite high-Q nanostructure adopted in this patent has a narrower resonance absorption peak (about 5 nm) than the existing spherical non-porous probe tip, and has higher wavelength sensitivity, and is based on resonance between resonators of different substructures.
  • the mode competition mechanism, its local field enhancement effect is several orders of magnitude of the common structure. Therefore, it is particularly suitable for high-resolution micro-area small-signal near-field optical imaging. At the same time, it has a multi-physical signal measurement in-situ measurement function, which is bound to be widely used.
  • the object of the present invention is to overcome the deficiencies of the prior art and to propose a multifunctional near-field optical probe based on a plasmonic nano-nail structure.
  • the resolution can break through the diffraction limit. And its spatial resolution depends on the diameter of the tip, up to 10nm, breaking through the bottleneck of the prior art, in line with the characterization requirements of the sample.
  • a multifunctional near-field optical probe based on a plasmonic nano-nail structure of the present invention is composed of a nano-nail tip, a tapered fiber and a tuning fork; wherein the nano-nail tip is grown by the nanowire One or more plasmon structures with multiple resonance effects; one end of the nano-nail is inserted into the tapered fiber through the core opening of the fiber; the nano-nail tip and the tapered fiber tip surface are connected by a two-dimensional material to prevent oxidation At the same time, the nano staple tip is electrically connected to the metal conductive reflective layer on the surface of the tapered fiber.
  • the polarized light When in operation, the polarized light is obliquely incident on the nanoneedle tip, stimulating the conductive surface plasmon polariton (SPP) mode (electromagnetic signal).
  • SPP conductive surface plasmon polariton
  • the enhanced electromagnetic signal is conducted to the sample through the other end of the nano-nail, and after interacting with the sample, the electromagnetic signal with the near-field information of the sample is coupled into the tapered fiber through one end of the nano-nail to form a conduction mode optical signal, and It was eventually extracted by the photodetector.
  • the mechanical signal of the probe tip extracted by the tuning fork can also be fed back to the near-field microscope. While controlling the height of the needle tip in the Z direction, it can also be used to extract the topographical information of the sample surface.
  • the electrical signal between the nanoneedle tip and the sample can be measured by an external circuit to detect the electrical information on the surface of the sample.
  • the material of the nanowire is a metal or indium tin oxide semiconductor alloy surface plasmon material; the diameter of the nanowire is 1 to 100 nm, and the diameter thereof is directly related to the spatial resolution of the probe, and the smaller the diameter, the more the spatial resolution high;
  • the material of the plasmon structure having multiple resonance effects is a semiconductor alloy surface plasmon material such as metal or indium tin oxide; a nanostructure having one or more anisotropic topography, having multiple resonance effects
  • the plasmonic structure is the same as or different from the material of the nanowire.
  • the metal material is: gold, silver, copper or aluminum.
  • the nanostructure of the anisotropic morphology is a triangular piece, a tetrahedron, a hexagonal piece, a decahedron, a nanorod, a nanostar or a nano cone.
  • the core layer of the tapered fiber has an aperture, the aperture is slightly larger than the diameter of the nanowire on the nano-nail, and the size is about 1 to 10 times the diameter of the nanowire, and the end of the nanowire is located at 1 to 1000 nm in the tapered fiber.
  • the aperture of the core opening is smaller than the wavelength of the incident light, so that the optical signal in the optical fiber cannot be leaked through the opening of the core layer.
  • the material of the metal conductive reflective layer of the tapered fiber is a highly reflective conductive material, and the light in the fiber is limited to the core layer of the fiber through total internal reflection while ensuring electrical conduction between the nanoneedle tip and the tapered fiber. Loss of signal strength.
  • the tuning fork is rigidly coupled to the tapered fiber.
  • the tuning fork has a different resonant frequency for different probe configurations.
  • the distance between the tip of the nano-nail tip and the sample is different, and the intermolecular force of the probe is also different, which affects the working frequency of the tuning fork.
  • the feedback between the probe and the sample can be controlled by feedback adjustment of the collected operating frequency.
  • the surface topography information of the scanned sample is recorded during the feedback adjustment process.
  • the two-dimensional material is a two-dimensional material having electrical conductivity and optical transparency. While ensuring the electrical conduction between the nanoneedle tip and the tapered fiber, it does not affect the conduction of electromagnetic signals in the nano-nail, and further has the function of preventing the oxidation of the probe.
  • the two-dimensional materials are graphene, black phosphorus, and molybdenum disulfide.
  • the polarized light is obliquely incident on the tip of the nano-nail, and the surface of the conductive surface is excited by the plasmon mode, and the polarized light is a laser of adjustable single polarization state. Its wavelength is: 300-30000nm, covering the ultraviolet-visible-infrared band.
  • the additional circuit can be used to measure current or voltage changes caused by factors sensitive to various probes such as spatial position, material properties, environmental changes, and applied electric fields on the sample surface.
  • the present invention has the following advantages over the prior art:
  • the spatial resolution of conventional near-field probes is usually greater than 50 nm, which cannot meet the characterization requirements of samples obtained by ultra-high precision (about 10 nm) micro-nano structure processing.
  • the multifunctional near-field optical probe based on the plasmonic nano-nail structure proposed by the invention utilizes the surface plasmon effect of the nano-nail tip, and the resolution can break through the diffraction limit. And its spatial resolution depends on the diameter of the tip, up to 10nm, breaking through the bottleneck of the prior art, in line with the characterization requirements of the sample.
  • the existing probe excitation mode is single, and the weak signal extraction ability is weak for a special sample structure.
  • the invention provides a multifunctional near-field optical probe based on a plasmonic nano-nail structure, and the intensity of the received signal can be controlled by adjusting the polarization direction of the polarized light.
  • the electromagnetic modes of nanostructures with various anisotropy are competing with each other, which can generate narrow linewidth and high Q value resonance peaks, which makes the probe have ultra-high sensitivity wavelength selectivity and ultra-high local field enhancement effect. It is beneficial for the extraction of small signals at a single wavelength.
  • the existing near-field probe has a single excitation mode and a single function, and cannot be used for the extraction of multiple physical signals in situ.
  • the utility model provides a multifunctional near-field optical probe based on a plasmonic nano-nail structure, which has various working modes such as optical fiber excitation spatial light receiving, spatial optical excitation fiber receiving and optical fiber excitation fiber receiving;
  • the probe can simultaneously extract topographic information, near-field optical information and electrical information near the surface of the sample, and has a powerful multi-physics representation mode and rich function expansion methods.
  • the multifunctional near-field optical probe based on the plasmon nano-nail structure proposed by the invention can extend the working band to the mid-infrared through structural optimization, and the resolution depends on the tip extraction signal.
  • the tip size can effectively improve the spatial resolution and make up for the low resolution of existing infrared probes.
  • FIG. 1 is a schematic diagram showing the structure and operation mode of a multifunctional near-field optical probe based on a nano-nail structure.
  • the figure includes: nano staple tip 1, metal nanowire 11, plasmon structure 12 with multiple resonance effects, one end of nanonail 13 , the other end of nanonail 14 , tapered optical fiber 2 , optical fiber 21 , core opening 22
  • FIG. 2 is a schematic diagram of a plasmonic structure having multiple resonance effects.
  • the invention relates to a multifunctional near-field optical probe based on a plasmonic nano-nail structure, which is composed of a nano nail tip, a tapered fiber and a tuning fork.
  • the nanoneedle tip is composed of a nanowire and one or more plasmon structures having multiple resonance effects grown thereon.
  • One end of the nanonail is inserted into the tapered fiber through the core of the fiber.
  • the nano-nail and the tapered fiber tip surface are connected by a two-dimensional material, and the nano-nail tip and the metal conductive reflective layer on the surface of the tapered fiber are electrically connected while preventing oxidation.
  • the polarized light When in operation, the polarized light is obliquely incident on the nanoneedle tip, stimulating the conductive surface plasmon polariton (SPP) mode (electromagnetic signal).
  • SPP conductive surface plasmon polariton
  • the enhanced electromagnetic signal is conducted to the sample through the other end of the nano-nail, and after interacting with the sample, the electromagnetic signal with the near-field information of the sample is coupled into the tapered fiber through one end of the nano-nail to form a conduction mode optical signal, and It was eventually extracted by the photodetector.
  • the mechanical signal of the probe tip extracted by the tuning fork can also be fed back to the near-field microscope. While controlling the height of the needle tip in the Z direction, it can also be used to extract the topographical information of the sample surface.
  • the electrical signal between the nanoneedle tip and the sample can be measured by an external circuit to detect the electrical information on the surface of the sample.
  • the nanoneedle tip 1 is composed of a nanowire 11 with one or more plasmon structures 12 having multiple resonance effects grown thereon.
  • the material of the nanowire 11 is: a metal alloy such as gold, silver, copper or aluminum or a semiconductor alloy surface plasmon material such as indium tin oxide; the diameter of the nanowire 11 is 1 to 100 nm, and the diameter and the spatial resolution of the probe are The rate is directly related, the smaller the diameter, the higher the spatial resolution.
  • the plasmon structure 12 having multiple resonance effects may be one or more anisotropic nanoparticles, such as triangular, tetrahedral, hexagonal, decahedron, nanorod, nanostar, nanocone, etc.
  • the material is: metal such as gold, silver, copper, aluminum or the like, or a semiconductor alloy surface plasmon material such as indium tin oxide, and the material may be the same as or different from the nanowire 11.
  • the core opening 22 of the tapered fiber 2 has a diameter slightly larger than the diameter of the nanowire 11 on the nano-nail 1, and the size thereof is about 1 to 10 times the diameter 11 of the nanowire, and the end of the nanowire 11 is located at the tapered fiber.
  • the near-field electromagnetic signal is coupled into the fiber to form a conductive mode optical signal.
  • the aperture of the core opening 22 is smaller than the wavelength of the incident light such that optical signals in the optical fiber cannot escape through the core opening 22.
  • the material of the metal conductive light-reflecting layer 23 of the tapered fiber 2 is a highly reflective conductive material of aluminum or silver.
  • the light in the optical fiber 21 can be confined in the core of the optical fiber by total internal reflection while the structure is electrically conductive, thereby reducing the loss of signal strength.
  • the tuning fork 3 is rigidly connected to the tapered optical fiber 2.
  • the tuning fork 3 has a different resonant frequency for different probe configurations.
  • the spacing between the nanoneedle tip 1 and the sample 6 is different, and the intermolecular force of the probe is also different, which may affect the operating frequency of the tuning fork 3.
  • the distance between the probe and the sample 4 can be controlled by feedback adjustment of the collected operating frequency.
  • the feedback adjustment process can also record the surface topography information of the sample.
  • the two-dimensional material 4 is a two-dimensional material having conductivity and optical transparency such as graphene, black phosphorus, and molybdenum disulfide (MoS 2 ). While ensuring the electrical conduction between the nano staple tip 1 and the tapered optical fiber 2, the electromagnetic signal conduction in the nano-nail is not affected, and further the function of preventing the probe from being oxidized.
  • MoS 2 molybdenum disulfide
  • the polarized light 5 is a laser of a tunable single polarization state, and has a wavelength of 300-30000 nm covering the ultraviolet-visible-infrared band.
  • the additional circuit 8 can be used to measure current or voltage changes caused by factors sensitive to various probes such as spatial position, material properties, environmental changes, and applied electric fields on the surface of the sample 6.
  • a multifunctional near-field optical probe based on a plasmonic nano-nail structure proposed by the present invention is significantly different from a conventional optical-type perforated near-field probe.
  • Conventional apertured probes use the principles of guided wave optics to conduct or extract optical signals. This method must first form the mode light, limited by the diffraction limit, so the resolution is limited.
  • the optical signal is converted into a plasmon signal by using the transmission and resonance characteristics of the surface plasmon of the nano-nail to realize the sub-wavelength transmission without diffraction limit.
  • the transmission wavelength is narrow-band, high-transmittance, and will be transmitted at the end of the exit end.
  • the transmitted spot size is determined by the tip diameter of the nano-nail structure, so the resolution is higher than the conventional one.
  • the perforated probe is greatly improved.
  • the mechanism of this excitation is completely different from that of a metal-coated, non-porous probe.
  • Conventional metallized, non-porous probes utilize the localized plasmon mode of the tip structure to excite or extract optical signals.
  • the present invention utilizes a surface plasmon polariton of a nano-nail structure to conduct an optical signal that cannot pass through the fiber cone to the sample by converting it into a sub-wavelength surface plasmon. Therefore, the probe signal of the present invention is more directional, and the signal intensity attenuation caused by multi-directional scattering is avoided.
  • the multi-functional near-field optical probe based on the plasmonic nano-nail structure proposed by the invention has the advantages of high light transmittance and high excitation efficiency of the porous probe, and has a non-porous probe.
  • the advantage of high resolution It will break through the existing technology bottleneck and bring new technical support to the field of ultra-high resolution near-field optical imaging.
  • the structure of the multifunctional near-field optical probe of the nano-nail structure is shown in FIG. 1 , wherein the silver nano-nail tip 1 is composed of a silver nanowire 11 having a diameter of 10 nm and a length of 5 ⁇ m and two side lengths thereof are 150 nm. It is composed of a 200 nm silver triangle plate 12; a tapered fiber 2 composed of an optical fiber 21 and a surface-coated aluminum film 23; and a tuning fork 3 which is rigidly connected to the tapered optical fiber.
  • One end 13 of the silver nanonail was inserted into the opening 22) of the tapered probe, wherein the opening was 50 nm and the insertion depth was 100 nm.
  • the nano nail tip and the aluminum film are connected by a single layer of graphene (4).
  • the 1310nm single-polarized light (5) is obliquely incident on the nanoneedle tip, exciting the conductive surface plasmon polariton (SPP) mode, and by controlling the polarization direction of the incident light parallel to the nanowire direction, Strong local field enhancements.
  • the resonant signal is conducted to the sample (6) through the other end of the nano-nail (14).
  • the electromagnetic signal with the near-field information of the sample is coupled into the tapered fiber through one end of the nano-nail to form a conduction mode light.
  • Signal (7) is finally extracted by the photodetector.
  • the mechanical signal of the probe tip extracted by the tuning fork can also be fed back to the near-field microscope. While controlling the height of the needle tip in the Z direction, it can also be used to extract the topographical information of the sample surface.
  • the sample After extracting the sample topography information, the sample is grounded while the probe, the sample substrate (where the sample substrate is required to conduct) and the external circuit (8).
  • the electrical signal measurement mode in the non-contact mode measuring the same region again, the potential difference signal between different regions of the sample and the nanoneedle tip can be obtained, and the signal is the surface potential signal of the sample.
  • FIG. 2 illustrates various combinations of plasmon structures (12) having multiple resonance effects, which may be composed of a single silver triangle plate structure, or may be composed of a plurality of silver triangle plates of different sizes and directions to realize probes. Further enrichment and regulation of the resonant spectrum.

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Abstract

本发明是一种基于等离激元纳米钉结构的多功能近场光学探针，该探针由纳米钉针尖(1)、锥形光纤(2)和音叉(3)三部分构成；其中纳米钉针尖(1)由纳米线(11)与其上生长的一个或多个具有多重谐振效应的等离激元结构(12)构成；纳米钉一端(13)通过光纤(21)的芯层开孔(22)插入锥形光纤(2)中；纳米钉针尖(1)与锥形光纤(2)尖端表面通过二维材料(4)相连，在防氧化的同时，使纳米钉针尖(1)与锥形光纤(2)表面的金属导电反光层(23)形成电学导通。因此，我们提出的探针具有波长、偏振选择性(敏感性)，突破了现有近场探针的技术瓶颈，大幅提高了近场光学探针的分辨率，可同时进行样品近场光学信息、形貌信息、电信号信息的提取。

Description

一种基于等离激元纳米钉结构的多功能近场光学探针 技术领域
本发明涉及近场显微成像领域、波导领域和纳米材料领域，特别涉及一种基于等离激元纳米钉结构的多功能近场光学探针。
背景技术
超高分辨率的显微表征技术是人们研究微观纳米结构的重要手段。然而，采用光学透镜组成像的传统显微方式，受到衍射极限的限制，分辨率无法突破波长量级，严重制约了纳米科技的发展。为此人们寻求利用波长更短的电子或离子为探测载体，制造分辨率更高的显微镜(如扫描电子显微镜等)。电子显微镜相较于光学显微镜，虽然在分辨率方面取得了重大的突破，但其依然存在着诸多弊端，如：样品一般具有较好的导电性，对绝缘体样品和溶液样品则无法使用；需要一定的真空环境；高分辨的成像模式必须使用高电压的电子束，对样品破坏性强等。因此，对样品与环境无特殊需求，非接触式、无损探测的近场光学显微技术越来越受到人们的青睐。
近场光学显微技术的分辨率与近场探针的拓扑结构、材料特性等密切相关。为了获得样品高分辨率的信息，一方面，必须使通过探针的光束在横向上尽可能的受到限域；另一方面，也要使通过限制区域的光通量尽可能的大，以得到高信噪比。
传统的近场探针分为有孔的光纤探针跟无孔的介质探针两大类。其中最常见的是有孔光纤探针。根据导波光学原理，光纤探针的针尖的几何形状和通过探针开孔的光流量(即光的传输效率)有关，从而也与分辨率有关。因此，为提高分辨率，对于光纤探针必须注意改进探针的针尖几何形状。但是，光纤探针分辨率的理论极限是12nm，而现今主流的热拉伸法制得的探针开孔尺寸也不能小于10nm。这严重制约着高分辨(小于10nm)的近场光学探针的发展。
无孔探针是探针顶端没有开孔的探针。因此，可避免光纤探针的固有缺陷。特别是，其针尖可以看作是与样品表面发生相互作用的一个或几个偶极子，从而获得超高的光学限域和局域场增强效果。同时，其分辨率受针尖的几何尺寸影响，可以突破10nm的瓶颈，因此无孔探针在提高空间分辨率方面有着巨大潜力。 但现有的无孔针尖大多为各向同性的球形，共振增强谱峰宽，光场局域效果有限，因此得到的光强信号较弱，影响探测图像的衬度。因此如何克服上述两类探针的局限，在提升分辨率的同时提高探测信号响应灵敏度是现今近场探针，乃至光学显微镜领域亟待解决的关键技术问题。
另一方面，现今的探针只针对单一功能设计。能同时测量样品光学、电学、形貌等多物理场信息的复合多功能探针的出现，必将提高纳米原位表征领域的技术革新，催生出更多新奇现象的发现及应用。
本专利所采用的复合高Q值纳米结构，相对于现有的球形无孔探针针尖，共振吸收峰更窄(约5nm)，波长敏感性更强，同时基于不同子结构谐振腔间的谐振模式竞争机制，其局域场增强效果是普通结构的数个数量级。因此，特别适合于高分辨率的微区小信号近场光学成像。同时其具有多物理信号测量原位测量功能，必将获得广泛的应用。
发明内容
技术问题：本发明的目的是为了克服已有技术的不足之处，提出了一种基于等离激元纳米钉结构的多功能近场光学探针。利用纳米钉针尖的表面等离激元效应，分辨率可突破衍射极限。且其空间分辨率取决于尖端的直径，可达10nm，突破了现有技术的瓶颈，与样品的表征需求相符合。
技术方案：本发明的一种基于等离激元纳米钉结构的多功能近场光学探针，由纳米钉针尖、锥形光纤和音叉三部分构成；其中纳米钉针尖由纳米线与其上生长的一个或多个具有多重谐振效应的等离激元结构构成；纳米钉一端通过光纤的芯层开孔插入锥形光纤中；纳米钉针尖与锥形光纤尖端表面通过二维材料相连，在防氧化的同时，使纳米钉针尖与锥形光纤表面的金属导电反光层形成电学导通。
处于工作状态时，偏振光斜入射到纳米钉针尖上，激励起传导型的表面等离极化激元(SPP)模式(电磁信号)。通过控制入射光的频率(可覆盖紫外-可见-红外波段)及偏振方向，对于不同结构的针尖，可在特定波长及偏振方向形成具有超高Q值的谐振峰，提高探测信号的灵敏度。这一增强了的电磁信号通过纳米钉另一端传导到样品，在与样品相互作用后，带有样品近场信息的电磁信号通过纳米钉一端耦合进锥形光纤中形成传导模式的光信号，并最终被光电探测器提取到。同时，通过音叉提取到的探针针尖力学信号还可反馈给近场显微镜，在控制针尖Z方向高度的同时，也可用来提取样品表面的形貌信息。当样品接地时，可通过外加电路测量纳米钉针尖与样品间的电信号，来探测样品表面的电学 信息。
其中，
所述纳米线的材料为金属或氧化铟锡半导体合金表面等离激元材料；纳米线的直径为1～100nm，其直径与探针的空间分辨率直接相关，直径越小，空间分辨率越高；
所述具有多重谐振效应的等离激元结构的材料为金属或氧化铟锡等半导体合金表面等离激元材料；为一种或多种各向异性形貌的纳米结构，具有多重谐振效应的等离激元结构与纳米线的材料相同或不同。
所述金属材料料为：金、银、铜或铝。
所述所述各向异性形貌的纳米结构为三角片、四面体、六角片、十面体、纳米棒、纳米星或纳米锥。
所述锥形光纤的芯层开孔，孔径略大于纳米钉上纳米线的直径，其大小约为纳米线直径的1～10倍，同时纳米线的端点位于锥形光纤内1～1000nm处，以便将近场电磁信号耦合入光纤中，形成传导模式的光信号；芯层开孔的孔径小于入射光的波长，使得光纤中的光信号无法通过芯层的开孔泄露出来。
所述锥形光纤的金属导电反光层的材料为高反光导电材料，在保障纳米钉针尖与锥形光纤电学导通的同时，将光纤中的光通过全内反射限制在光纤芯层中，降低信号强度的损失。
所述音叉与锥形光纤刚性连接。对于不同的探针结构，音叉的共振频率不同。同时纳米钉针尖与样品间的间距不同，探针所受到的分子间作用力也不同，从而会影响音叉的工作频率。通过对收集到的工作频率进行反馈调节，可控制探针与样品间的间距。同时，反馈调节过程中记录所扫描样品的表面形貌信息。
所述二维材料为具有导电性及光学透明性的二维材料。在保障纳米钉针尖与锥形光纤电学导通的同时，还不影响纳米钉中电磁信号的传导，并且进一步还有防止探针氧化的功能。具体为二维材料为石墨烯、黑磷、二硫化钼。
所述的多功能近场光学探针处于工作状态时，偏振光斜入射到纳米钉针尖上，激励起传导型的表面等离极化激元模式，偏振光为可调单偏振态的激光，其波长为：300-30000nm，覆盖紫外-可见-红外波段。
所述外加电路可用于测量样品表面由于空间位置、材料属性、环境变化、外加电场等各种探针所敏感的因素影响引起的电流或电压变化。
有益效果：本发明与现有的技术相比具有以下的优点：
1传统的近场探针空间分辨率通常大于50nm，无法满足现今超高精度(10nm左右)的微纳结构加工工艺所获得的样品的表征需求。本发明所提出的一种基于等离激元纳米钉结构的多功能近场光学探针，利用纳米钉针尖的表面等离激元效应，分辨率可突破衍射极限。且其空间分辨率取决于尖端的直径，可达10nm，突破了现有技术的瓶颈，与样品的表征需求相符合。
2现有探针激励方式单一，针对特殊的样品结构下微弱信号的提取能力弱。本发明所提出的一种基于等离激元纳米钉结构的多功能近场光学探针，通过调节偏振光的偏振方向可控制接收信号的强度。并且多种形貌各向异性的纳米结构间电磁模式相互竞争，可产生窄线宽，高Q值的共振峰，使得探针具有超高灵敏度的波长选择性以及超高的局域场增强效果，有利于单波长下的微小信号的提取。
3现有近场探针激励方式单一，功能单一，无法胜任原位的多物理信号的提取工作。本发明所提出的一种基于等离激元纳米钉结构的多功能近场光学探针，具有光纤激励空间光接收、空间光激励光纤接收及光纤激励光纤接收等多种工作模式；同时通过该探针可以同时提取样品表面附近的形貌信息、近场光学信息及电学信息等，具有强大的多物理场表征方式及丰富的功能拓展方式。
4现有的红外近场探针尺寸大，分辨率低。本发明所提出的一种基于等离激元纳米钉结构的多功能近场光学探针，通过结构优化，可将工作波段拓展至中红外，同时由于是尖端提取信号，所以其分辨率取决于尖端尺寸，可有效提高空间分辨率，弥补现有红外探针分辨率低的缺陷。
附图说明
图1是一种基于纳米钉结构的多功能近场光学探针的结构及工作模式示意图。
图中有：纳米钉针尖1、金属纳米线11、具有多重谐振效应的等离激元结构12、纳米钉一端13、纳米钉另一端14、锥形光纤2、光纤21、芯层开孔22、金属导电反光层23、音叉3单层石墨烯4、偏振光5、样品6、传导模式的光信号7、外加电路8。
图2是具有多重谐振效应的等离激元结构的示意图。
具体实施方式
本发明是一种基于等离激元纳米钉结构的多功能近场光学探针，由纳米钉针尖、锥形光纤和音叉三部分构成。其中纳米钉针尖由纳米线与其上生长的一个或多个具有多重谐振效应的等离激元结构构成。纳米钉一端通过光纤的芯层插入锥 形光纤中。并且纳米钉与锥形光纤尖端表面通过二维材料相连，在防氧化的同时，可使纳米钉针尖与锥形光纤表面的金属导电反光层形成电学导通。处于工作状态时，偏振光斜入射到纳米钉针尖上，激励起传导型的表面等离极化激元(SPP)模式(电磁信号)。通过控制入射光的频率(可覆盖紫外-可见-红外波段)及偏振方向，对于不同结构的针尖，可在特定波长及偏振方向形成具有超高Q值的谐振峰，提高探测信号的灵敏度。这一增强了的电磁信号通过纳米钉另一端传导到样品，在与样品相互作用后，带有样品近场信息的电磁信号通过纳米钉一端耦合进锥形光纤中形成传导模式的光信号，并最终被光电探测器提取到。同时，通过音叉提取到的探针针尖力学信号还可反馈给近场显微镜，在控制针尖Z方向高度的同时，也可用来提取样品表面的形貌信息。当样品接地时，可通过外加电路测量纳米钉针尖与样品间的电信号，来探测样品表面的电学信息。
其中：
所述纳米钉针尖1由纳米线11与其上生长的一个或多个具有多重谐振效应的等离激元结构12构成。其中，纳米线11的材料为：金、银、铜、铝等金属或氧化铟锡等半导体合金表面等离激元材料；纳米线11的直径为1～100nm，其直径与探针的空间分辨率直接相关，直径越小，空间分辨率越高。具有多重谐振效应的等离激元结构12可为一种或多种各向异性形貌的纳米颗粒，如三角片、四面体、六角片、十面体、纳米棒、纳米星、纳米锥等，其材料为：金、银、铜、铝等金属或氧化铟锡等半导体合金表面等离激元材料，材料可与纳米线11相同，也可不同。
所述锥形光纤2的芯层开孔22，孔径略大于纳米钉1上纳米线11的直径，其大小约为纳米线直径11的1～10倍，同时纳米线11的端点位于锥形光纤内1～1000nm处，以便将近场电磁信号耦合入光纤中，形成传导模式的光信号。芯层开孔22的孔径小于入射光的波长，使得光纤中的光信号无法通过芯层开孔22泄露出来。
所述锥形光纤2的金属导电反光层23的材料为：铝或银的高反光导电材料。在保障结构导电的同时可以将光纤21中的光通过全内反射限制在光纤芯层中，降低信号强度的损失。
所述音叉3与锥形光纤2刚性连接。对于不同的探针结构，音叉3的共振频率不同。同时纳米钉针尖1与样品6间的间距不同，探针所受到的分子间作用力也不同，从而会影响音叉3的工作频率。通过对收集到的工作频率进行反馈调节， 可控制探针与样品4间的间距。同时，反馈调节过程也可记录下样品的表面形貌信息。
所述二维材料4为石墨烯、黑磷、二硫化钼(MoS 2)等具有导电性及光学透明性的二维材料。在保障纳米钉针尖1与锥形光纤2电学导通的同时，还不影响纳米钉中电磁信号的传导，并且进一步还有防止探针氧化的功能。
所述偏振光5为可调单偏振态的激光，其波长为：300-30000nm，覆盖紫外-可见-红外波段。
所述外加电路8可用于测量样品6表面由于空间位置、材料属性、环境变化、外加电场等各种探针所敏感的因素引起的电流或电压变化。
在光信号的传导及提取方式方面本发明所提出的一种基于等离激元纳米钉结构的多功能近场光学探针与传统的光纤型有孔近场探针有着显著的区别。传统有孔探针利用导波光学原理传导或提取光信号。该方法必须先形成模式光，受衍射极限限制，因此分辨率有限。本发明中，通过控制锥形光纤的纤芯大小在亚波长范围内，使得其中传输的光无法从光纤锥中向下透射。同时，利用纳米钉的表面等离极化激元的传输和谐振特性，将光信号转换为等离激元信号，实现不受衍射极限的亚波长透射。鉴于纳米钉特有的多谐振竞争特性，透射波长是窄带的，高透过率的，且将在出射端的端点透射下去，其透射光斑大小由纳米钉结构的尖端直径所决定，所以分辨率比传统有孔探针大大提高。
此外，这种激励的机制和单纯的金属镀膜的无孔探针的工作方式也是完全不同的。传统的金属镀膜的无孔探针利用尖端结构的局域等离激元模式激励或提取光信号。而本发明利用的是纳米钉结构的表面等离极化激元，将本不能透过光纤锥的光信号，通过转换成亚波长表面等离极化激元的方式传导至样品。因此本发明的探针信号的导向性更强，避免了多方向散射带来的信号强度衰减。
综上，本发明所提出的一种基于等离激元纳米钉结构的多功能近场光学探针既具有有孔探针通光率高、激发效率高的优点，又具有无孔探针的高分辨率的优势。必将突破现有技术瓶颈，为超高分辨率的近场光学成像领域带来新的技术支持。
下面通过具体实施例和对比例进一步说明本发明：
实施例：
纳米钉结构的多功能近场光学探针的结构如图1所示，其中银纳米钉针尖1，它由直径为10nm长为5μm的银纳米线11及其上的两个边长分别为150nm和 200nm的银三角板12组成；锥形光纤2，它由光纤21和表面镀的铝膜23构成；音叉3，它与锥形光纤刚性连接。银纳米钉一端13插入锥形探针的开孔22)中，其中开孔为50nm，插入深度为100nm。同时纳米钉针尖与铝膜通过一次单层石墨烯(4)相连。
1310nm的单偏振光(5)斜入射到纳米钉针尖上，激励起传导型的表面等离极化激元(SPP)模式，通过控制入射光的偏振方向与纳米线方向平行，可获得具有超强的局域场增强效果。这一谐振信号通过纳米钉另一端(14)传导到样品(6)，在与样品相互耦合后，带有样品近场信息的电磁信号通过纳米钉一端耦合进锥形光纤中形成传导模式的光信号(7)，并最终被光电探测器提取到。同时，通过音叉提取到的探针针尖力学信号还可反馈给近场显微镜，在控制针尖Z方向高度的同时，也可用来提取样品表面的形貌信息。
在提取样品形貌信息后，将样品接地，同时将探针、样品衬底(此时要求样品衬底导电)与外加电路(8)。采用非接触模式中的电学信号测量模式，再一次测量同一区域，可得到样品不同区域与纳米钉针尖间的电势差信号，该信号为样品的表面电势信号。
图2示意了具有多重谐振效应的等离激元结构(12)的多种组合方式，可由单个银三角板结构构成，也可由多个大小不一和方向不同的银三角板结构组成，以实现探针的谐振光谱的进一步丰富和调控。

Claims (10)

  1. 一种基于等离激元纳米钉结构的多功能近场光学探针，其特征在于：该探针由纳米钉针尖(1)、锥形光纤(2)和音叉(3)三部分构成；其中纳米钉针尖(1)由纳米线(11)与其上生长的一个或多个具有多重谐振效应的等离激元结构(12)构成；纳米钉一端(13)通过光纤(21)的芯层开孔(22)插入锥形光纤(2)中；纳米钉针尖(1)与锥形光纤(2)尖端表面通过二维材料(4)相连，在防氧化的同时，使纳米钉针尖(1)与锥形光纤(2)表面的金属导电反光层(23)形成电学导通。
  2. 如权利要求1所述的一种基于等离激元纳米钉结构的多功能近场光学探针，其特征在于：所述纳米线(11)的材料为金属或氧化铟锡半导体合金表面等离激元材料；纳米线(11)的直径为1～100nm，其直径与探针的空间分辨率直接相关，直径越小，空间分辨率越高；
  3. 如权利要求1所述的一种基于等离激元纳米钉结构的多功能近场光学探针，其特征在于：所述具有多重谐振效应的等离激元结构(12)的材料为金属或氧化铟锡等半导体合金表面等离激元材料；为一种或多种各向异性形貌的纳米结构，具有多重谐振效应的等离激元结构(12)与纳米线(11)的材料相同或不同。
  4. 如权利要求2或3所述的一种基于等离激元纳米钉结构的多功能近场光学探针，其特征在于：所述金属材料料为：金、银、铜或铝。
  5. 如权利要求3所述的一种基于等离激元纳米钉结构的多功能近场光学探针，其特征在于：所述所述各向异性形貌的纳米结构为三角片、四面体、六角片、十面体、纳米棒、纳米星或纳米锥。
  6. 如权利要求1所述的一种基于等离激元纳米钉结构的多功能近场光学探针，其特征在于：所述锥形光纤(2)的芯层开孔(22)，孔径略大于纳米钉(1)上纳米线(11)的直径，其大小约为纳米线直径(11)的1～10倍，同时纳米线(11)的端点位于锥形光纤内1～1000nm处，以便将近场电磁信号耦合入光纤中，形成传导模式的光信号；芯层开孔(22)的孔径小于入射光的波长，使得光纤中的光信号无法通过芯层开孔(22)泄露出来。
  7. 如权利要求1所述的一种基于等离激元纳米钉结构的多功能近场光学探针，其特征在于：所述锥形光纤(2)的金属导电反光层(23)的材料为高反光导电材料，在保障纳米钉针尖(1)与锥形光纤(2)电学导通的同时，将光纤(21) 中的光通过全内反射限制在光纤芯层中，降低信号强度的损失。
  8. 如权利要求1所述的一种基于等离激元纳米钉结构的多功能近场光学探针，其特征在于：所述音叉(3)与锥形光纤(2)刚性连接。
  9. 如权利要求1所述的一种基于等离激元纳米钉结构的多功能近场光学探针，其特征在于：所述二维材料(4)为石墨烯、黑磷、二硫化钼。
  10. 如权利要求1所述的一种基于等离激元纳米钉结构的多功能近场光学探针，其特征在于：所述的多功能近场光学探针处于工作状态时，偏振光(5)斜入射到纳米钉针尖(1)上，激励起传导型的表面等离极化激元模式，偏振光(5)为可调单偏振态的激光，其波长为：300-30000nm，覆盖紫外-可见-红外波段。
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