CN203164205U - Surface plasma longitudinal field scanning near-field optic microscope device - Google Patents

Abstract

The utility model provides a surface plasma longitudinal field scanning near-field optic microscope device. The device is provided with a surface plasma excitation unit (1), a scanning control unit (2) and a detection unit (3); after being focused through a high numerical aperture objective lens (6), incident light excites an SPP field on an interface of a metal membrane and air, raman signals and the SPP field interfere with each other to form a stationary field of the SPP field around a focus; the scanning control unit (2) can achieve three-dimensional scanning and positioning for an atomic force microscope (AFM) metal probe (5) by means of an AFM controller (4); and the detection unit (3) achieves three-dimensional measurement and analysis for a longitudinal field component of a surface plasma field.

Description

A surface plasmon longitudinal field scanning near-field optical microscope device

technical field

The utility model belongs to the optical sensing and imaging technical field of near-field optical detection, in particular to a detection device for surface plasma longitudinal field. the

Background technique

In the prior art, the fine structure and fluctuation information of an object smaller than the diffraction limit under near-field conditions is closely related to the non-radiative field bound on the surface of the object. On the one hand, the non-radiative field in the near-field region contains detailed information of the object structure ; on the other hand, since the field strength of this field decays exponentially with the distance from the surface, it cannot be detected in the far field, that is, traditional optical detection techniques. This contradiction concentrates the core problem of near-field optics on the technology of detecting the non-radiation field bound on the surface of the object, and transmitting the non-radiation field in the form of radiation field without distortion, and receiving it. Since surface plasmon resonance can effectively enhance the intensity of the local field and has a series of novel characteristics, the near-field detection of surface plasmons (Surface Plasmons Polaritons, SPPs) is an important issue in near-field optics. SPPs in the near-field region contain a wealth of information reflecting the fine structure and optical properties of objects. Therefore, the detection technology of SPPs is not only important for understanding the excitation and propagation characteristics of surface plasmons, but also for SPPs sensing and imaging technologies. guiding significance. Due to the surface wave characteristics of SPPs, the electric field strength of SPPs exhibits an exponential decay form in the direction perpendicular to the interface, so traditional optical microscopy methods cannot image them. the

At present, the more common instrument for measuring the near-field distribution is the scanning near-field optical microscope (SNOM), but there are some defects and deficiencies in the near-field detection of surface plasmons by using SNOM: , in general only the transverse component of the light field in the near-field region can be detected. Studies have shown that only when the longitudinal component of the field to be measured is 30 times larger than the transverse component, can the longitudinal component of the near field be effectively detected. For SPPs, the longitudinal component is dominant, but the proportion of the longitudinal field to the total field is different under different conditions, but overall, there is still a gap of 30 times between the longitudinal field component and the transverse field component, so it is impossible to use SNOM to conduct longitudinal field analysis. Effective detection of the field. Second, transmitted light has a great influence on the imaging results. Since the transmitted light can also be effectively coupled to the fiber optic probe of SNOM, the near-field distribution obtained by using SNOM is the superposition of SPPs and transmitted light, which affects the detection quality of SPPs light field to a certain extent. Especially in the case of high numerical aperture focusing, the intensity of the transmitted light is even greater than that of the generated SPPs, thus greatly reducing the reliability of detection. Especially for the light field near the focal point, perfect SPPs light field imaging has not been obtained so far. Therefore, it is of great significance to research and develop a set of ultra-high-resolution imaging technology that can effectively detect the near-field longitudinal component and can well eliminate the influence of transmitted light. the

Utility model content

The utility model improves on the problems existing in the above-mentioned prior art, that is, the technical problem to be solved by the utility model is to provide a surface plasmon longitudinal field scanning near-field optical microscope device, which realizes ultra-high resolution when using the device The near-field electric field longitudinal component of the rate is scanned for probing. the

The surface plasmon longitudinal field detection device of the present utility model includes: a surface plasmon longitudinal field scanning near-field optical microscope device, which has a surface plasmon excitation unit 1, a scanning control unit 2 and a detection unit 3; a surface plasmon excitation unit 1 Including: excitation light source, beam splitter 7, high numerical aperture objective lens 6, glass slide coated with 45nm silver film, three-dimensional scanning platform; There are Raman molecules; the light beam emitted by the excitation light source passes through the beam splitter 7, and the high numerical aperture objective lens 6 is irradiated on the glass slide adsorbed with Raman molecules; the scanning control unit 2 includes: AFM metal probe 5, AFM controller 4, computer AFM controller 4 controls and connects AFM metal probe 5; computer control connects AFM controller 4; detection unit 3 includes: spectrum analyzer 11, photomultiplier tube 10, beam splitter 8, CCD and computer; beam splitter 8 connects Spectrum analyzer 11, photomultiplier tube 10; Spectrum analyzer 11 connects CCD; CCD and photomultiplier tube 10 connect computer; Spectrum analyzer 11 connects CCD; CCD and photomultiplier tube 10 connect computer;

What spectrometer (11) analyzes is Raman spectrum;

It has a surface plasmon excitation step, a scanning control step and a detection step; the surface plasmon excitation step is to adsorb Raman molecules through self-assembly on the interface between the metal film and the air, and after the incident light is focused by the high numerical aperture objective lens (6) on the gold The SPP field is generated at the interface between the film and the air. Under the action of the SPP field, the Raman molecules on the gold film emit Raman signals, and their mutual interference forms a standing wave field of SPPs near the focus. The characteristics of the SPP field are obtained by analyzing the Raman signal;

The scan control step utilizes the AFM controller (4) to realize three-dimensional scanning and positioning of the AFM metal probe (5);

The detection step realizes the three-dimensional measurement and analysis of the longitudinal field component of the surface plasma field. the

It has a surface plasmon excitation step, a scanning control step and a detection step; the surface plasmon excitation step is to coat the Raman molecule on the interface between the metal film and the air, and after the incident light is focused by the high numerical aperture objective lens 6, it is on the interface between the gold film and the air The SPP field is generated, and under the action of the SPP field, the Raman molecules on the gold film emit Raman signals, and their mutual interference forms a standing wave field of SPPs near the focus, and the characteristics of the SPP field are obtained by analyzing the Raman signal; the scanning control step uses The AFM controller 4 can realize three-dimensional scanning and positioning of the AFM metal probe 5;

The detection step realizes the three-dimensional measurement and analysis of the longitudinal field component of the surface plasma field. the

In the surface plasmon excitation unit, the TM light waves meeting the surface plasmon excitation conditions are focused by a high numerical aperture (N.A=1.49) objective lens, which can form an ATR (attenuated total reflection, Attenuated Total Reflection) structure, so that it can be on the silver film (or gold film; Surface plasmons are generated on the surface of the self-made, average film thickness difference is 0.3nm), and the excitation light of different polarization states produces surface plasmon distributions with different distribution patterns on the surface of the metal film. the

The scanning control unit can realize the three-dimensional scanning and positioning of the AFM metal probe by using the AFM controller. When the AFM metal probe tip is controlled to be close to the SPPs on the surface of the metal film, the interaction between the SPPs and the metal probe tip can effectively excite the local Surface plasmon (LSP), which greatly enhances the electric field at the tip of the metal needle tip. When Raman molecules are adsorbed on the tip of the metal probe through self-assembly, the Raman signal is enhanced by more than 10 ⁸ times due to the existence of a highly localized and significantly enhanced coupling field; when considering the influence of transmitted light, the corresponding SPPs excited The Raman signal intensity is 20 times that of the signal excited by transmitted light, and the Raman signal intensity of the coupling field between SPPs and LSP is nearly 2 orders of magnitude higher than that excited by SPPs alone, so the influence of transmitted light can basically be ignored. .

In the detection unit, the surface plasmon generated on the surface of the metal film contains two parts: a longitudinal component and a transverse component. The ratio of the longitudinal component and the transverse component of SPPs is determined by the ratio of the dielectric constant of the metal and its surrounding dielectric, namely: |E _z | ² /|E _r | ² = |ε _m |/ε _d , in the visible range, for gold and silver, the two most commonly used metals to excite surface plasmons, the ratios are 0.83, 21.78, respectively And 2.923, 26.3, the size of this ratio does not meet the lower limit of 30 times that the longitudinal field is the transverse field, so it cannot be directly detected by conventional methods. The detection unit of the utility model realizes Raman enhancement by means of the interaction between SPPs and metal probe tips, and passes the Raman signal from above the metal film through the high numerical aperture oil immersion objective lens through surface plasmon-coupled emission (SPCE) Directional coupling to the beam splitter 1, and then enter the CCD and photomultiplier tube respectively through the beam splitter 2, and the collection of Raman signals is controlled by the computer, and then the single-point longitudinal field component measurement of the surface plasmon field is obtained. Controlling the AFM metal probe for three-dimensional scanning can realize three-dimensional measurement and analysis of the longitudinal field component of the surface plasmon field. The resolution of the entire longitudinal field detection result is below 50nm, and the acquisition process time of each longitudinal field distribution image is only 1-2 minutes. The intuitive longitudinal field distribution can be obtained by deconvoluting the images acquired by the CCD, which can form a good complement to the longitudinal field distribution obtained by using the photomultiplier tube.

The surface plasmon longitudinal field detection method of the utility model includes: coating a single layer of Raman molecules on the metal film and air interface through self-assembly, and when the incident light is focused by a high numerical aperture objective lens, it will be excited at the metal film and air interface SPPs, which interfere with each other to form a standing wave field of SPPs near the focal point. When the AFM metal probe tip attached with Raman molecules is close to the standing wave field of the SPPs, due to the interaction between the SPPs and the metal probe tip, the localized surface plasmon (LSP) can be effectively excited, so that the electric field at the tip of the metal tip has been greatly enhanced. Since the orientation of the gap structure (metal film-gap-metal probe structure) of the metal film-AFM metal probe is consistent with the orientation of the longitudinal field component of SPPs, the LSP can be fully excited, and the transverse field does not participate in the excitation of the LSP. When the Raman The coupled field-excited Raman signals of SPPs and LSPs are also greatly enhanced when the molecules are attached to the needle tip. the

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; RS</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Proportional;</span>{\mathrm{<span\; class="notranslate">\; N\&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; SERS</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; loc</span>}}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 4</span>}}}{{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; SP</span>}}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 4</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; SP</span>}}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; N\&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; SERS</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; RE</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; SP</span>}}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

where I _RS is the Raman signal intensity, E _loc is the field strength of the coupling electromagnetic field between SPPs and LSP, e _sp is the field strength of the SPPs field that excites LSP, and RE is the Raman enhancement factor.

From the above principle, it can be obtained that the Raman signal intensity is proportional to the SPPs electric field intensity at the position of the needle tip, and since the transverse component of SPPs is basically irrelevant to the excitation of LSP, and the main body of the SPPs electric field intensity is its longitudinal component, so according to Raman The relationship between the signal strength and the longitudinal electric field strength of the SPPs at the position of the needle tip can be used to obtain the longitudinal field strength distribution at the corresponding position; and then perform high-precision three-dimensional scanning on the experimental platform, and at the same time introduce the Raman signal into the photomultiplier tube for secondary amplification , the effective, precise and very fast measurement of the longitudinal component of surface plasmons in the entire near-field range can be realized. the

The utility model provides a method and device for high-precision and high-sensitivity measurement of the surface plasma longitudinal field. By adopting SPPs and LSP coupling Raman spectrum enhancement technology, the interference caused by external environmental factors is effectively reduced, and the longitudinal field is improved. Measurement reliability and stability. The utility model can be extended to the detection of the longitudinal component of the ordinary light field, is easy to be applied in different types of SPR coupling schemes, and has simple system design and convenient operation. the

Description of drawings:

Figure 1 Schematic diagram of the surface plasmon longitudinal field detection device;

Fig. 2 is a schematic diagram of the simulated results of the experiment by the finite difference time domain method;

Fig. 3 Schematic diagram of the comparison between the SPPs field and its horizontal and vertical components in the simulation results and the experimental results;

Fig. 4 Scanning results of the standing wave field of SPPs near the focal point: a, b, and c are the longitudinal field distribution of SPPs excited by the vortex beam with a topological charge of 1 for linearly polarized light and radially polarized light, respectively. d, e, f, are simulation results according to Richard-wolf vectorial method (Richard-Wolf vector integral theory);

Figure 5-1 Experimental results of center half-width of longitudinal field components;

Figure 5-2 Schematic diagram of the repeatable experimental results of the center width at half maximum of the longitudinal field component. the

Detailed ways:

Below in conjunction with accompanying drawing and embodiment the utility model is further described. the

The basic idea of the utility model is to achieve Raman enhancement by means of the interaction between SPPs and metal probe tips, and to indirectly detect the longitudinal field distribution with the Raman signal intensity according to the proportional relationship between the Raman signal intensity and the SPPs longitudinal component. the

Embodiment: as shown in Figure 1, 2, 3, 4, 5-1, 5-2,

A surface plasmon longitudinal field scanning near-field optical microscope device has a surface plasmon excitation unit 1, a scanning control unit 2 and a detection unit 3; the surface plasmon excitation unit 1 includes: an excitation light source, a beam splitter 7, a high numerical aperture Objective lens 6, a glass slide coated with 45nm silver film, and a three-dimensional scanning platform; the glass slide coated with a 45nm silver film is set on the three-dimensional scanning platform, and Raman molecules are adsorbed on it through self-assembly; the beam emitted by the excitation light source passes through the beam splitter Device 7, high numerical aperture objective lens 6 is irradiated on the glass slide that is adsorbed with Raman molecule; Scanning control unit 2 includes: AFM metal probe 5, AFM controller 4, computer; AFM controller 4 controls and connects AFM metal probe 5; Computer control connects AFM controller 4; Detection unit 3 includes: spectrum analyzer 11, photomultiplier tube 10, beam splitter 8, CCD and computer; Beam splitter 8 connects spectrum analyzer 11, photomultiplier tube 10; Spectrum analyzer 11 connect CCD; CCD and photomultiplier tube 10 connect computer;

What spectrometer (11) analyzes is Raman spectrum;

It has a surface plasmon excitation step, a scanning control step and a detection step; the surface plasmon excitation step is to adsorb Raman molecules through self-assembly on the metal film and air interface, after the incident light is focused by a high numerical aperture objective lens (6) The SPP field is generated at the interface between the gold film and the air. Under the action of the SPP field, the Raman molecules on the gold film emit Raman signals, which interfere with each other to form a standing wave field of SPPs near the focus. The SPP field is obtained by analyzing the Raman signal. features;

The scan control step utilizes the AFM controller (4) to realize three-dimensional scanning and positioning of the AFM metal probe (5);

The detection step realizes the three-dimensional measurement and analysis of the longitudinal field component of the surface plasma field. the

It has a surface plasmon excitation step, a scanning control step and a detection step; the surface plasmon excitation step is to coat the Raman molecule on the interface between the metal film and the air, and after the incident light is focused by the high numerical aperture objective lens 6, it is on the interface between the gold film and the air Generate an SPP field, under the action of the SPP field, the Raman molecules on the gold film emit Raman signals, and their mutual interference forms a standing wave field of SPPs near the focus, and the characteristics of the SPP field are obtained by analyzing the Raman signal;

The scan control step utilizes the AFM controller 4 to realize three-dimensional scanning and positioning of the AFM metal probe 5;

The detection step realizes the three-dimensional measurement and analysis of the longitudinal field component of the surface plasma field. the

And in order to simplify the device, the AFM metal scanning head system is replaced by silver nanospheres with a diameter of 60nm, and the Raman molecules are placed between the nanospheres and the metal film. Due to the longitudinal arrangement between the nanospheres and the metal film, only the longitudinal component of the electric field can effectively excite the LSP, and the electric field is bound in the gap between the nanospheres and the metal film where the Raman molecules are located. So this method has exactly the same function as the AFM metal scanning head system. Through the analysis of the experimental results of the simplified device, the feasibility, effectiveness and practicability of the surface plasmon longitudinal field scanning microscope system can be evaluated. It can be seen from Figure 2 that due to the introduction of the near-field detection device (metal ball, AFM metal probe 5), the field distribution of the SPPs field does not change, and only the energy gathers between the detection device and the gold film. The experiment was simulated by the finite difference time domain method, and compared with the experimental results, as shown in Figure 3, without loss of generality, using the above device, respectively for linearly polarized light, radially polarized light, and topological charge 1 The numerical simulation and the actual measurement of the corresponding SPPs longitudinal field were carried out for the vortex beam, and the results are shown in Fig. 4. The standing wave field of SPPs measured according to this experimental scheme is in good agreement with the numerically simulated longitudinal electric field distribution, with high accuracy. For SPPs excited by radially polarized light with a wavelength of 632.8nm, the central maximum half-maximum width of the longitudinal field component in the experimental detection results is 184.3nm, as shown in Figures 5-1 and 5-2, with fifty samples as A group of repeated experiments, the results basically meet the normal distribution, the center of the longitudinal field maximum value at half maximum is 188.93nm (0.355λ ₀ , correspondingly, 0.099λ ₀ ² ) than its typical value of 0.16λ ₀ ² 38% smaller with a standard deviation of 6.76nm. This is of great significance for improving the resolution of the system. At the same time, due to the significant Raman enhancement effect and the secondary amplification of the photomultiplier tube, the Raman signal is significantly amplified, thereby effectively reducing the integration time required for scanning imaging, which greatly improves the practicality of the system of the present invention. sex. In a word, according to our experiment results, the feasibility, effectiveness and practicality of the system of the present utility model have been verified.

Apparently, the above-mentioned embodiments of the present utility model are only examples for clearly illustrating the present utility model, rather than limiting the implementation manner of the present utility model. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. And these obvious changes or variations derived from the spirit of the present utility model are still within the protection scope of the present utility model. the

Claims (2)

1. a surface plasma longitudinal field optical microscope for scanning near field device is characterized in that, has surface plasma and excites unit (1), scan control unit (2) and detecting unit (3); Described surface plasma excites unit (1) to comprise: excitation source, beam splitter (7), high-NA objective (6), the slide that is coated with the 45nm silverskin, 3-D scanning platform; The slide of the described 45nm of being coated with silverskin is arranged on the described 3-D scanning platform, is adsorbed with Raman molecular by self assembly on it; The light beam that described excitation source sends passes described beam splitter (7), high numerical aperture journey object lens (6) and is radiated on the described slide that is adsorbed with Raman molecular; Described scan control unit (2) comprising: AFM metal probe (5), AFM controller (4), computing machine; The described AFM metal probe of described AFM controller (4) control linkage (5); Described computer control connects described AFM controller (4); Described detecting unit (3) comprising: spectroanalysis instrument (11), photomultiplier (10), beam splitter (8), CCD and computing machine; Described beam splitter (8) connects described spectroanalysis instrument (11), photomultiplier (10); (11 connect described CCD to described spectroanalysis instrument; Described CCD is connected described computing machine with photomultiplier (10).

2. surface plasma longitudinal field optical microscope for scanning near field device according to claim 1 is characterized in that: what described spectroanalysis instrument (11) was analyzed is Raman spectrum.

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