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被广泛报道的--纳米级光学显微镜,是什么东东?  

2011-05-08 08:58:12|  分类: 默认分类 |  标签: |举报 |字号 订阅

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驰奔 编辑 (转载请注明)

以下解读Published 在1 Mar 2011《自然通讯 Nature communication》杂志上的 纳米光学显微镜

Optical virtual imaging at 50 nm lateral resolution with a white-light nanoscope 
Zengbo Wang1 , Wei Guo1 , 2, Lin Li1 , Boris Luk’ yanchuk3 , Ashfaq Khan1 , Zhu Liu2 , Zaichun Chen3 , 4 &
Minghui Hong 3 , 4

被广泛报道的--纳米级光学显微镜,是什么东东? - 驰奔 - ---DEMA 驰奔---
Figure 1 | Experimental configuration of white-light microsphere nanoscope with 波长 / 8 – 波长/ 14 imaging resolution. Schematic of the  transmission mode microsphere superlens integrated with a classical optical microscope. The spheres collect the near-field object information and form virtual images that can be captured by the conventional lens.
白光纳米显微镜试验结构,具有八分之一到14分之一波长的图像分辨率(远场光学分辨率为2分之一波长)。透射模式微米球超级透镜和传统的光学显微镜结合的原理图。微米球透镜用于收集近场目标的信息,形成能够被传统镜头捕获的虚像。

 
被广泛报道的--纳米级光学显微镜,是什么东东? - 驰奔 - ---DEMA 驰奔---

  ( a ) Microsphere superlens imaging of 360-nm-wide lines spaced 130 nm apart (top left image taken by scanning electron microscope (SEM)), the optical nanoscope (ON) image (top right image) shows that the lines are clearly resolved. ( b ) A gold-coated fishnet AAO sample imaged with a microsphere ( a = 2.37 μ m, borders of two spheres are shown by white lines) superlens. The nanoscope clearly resolves the pores that are 50 nm
in diameter and spaced 50 nm apart (bottom left SEM image). The size of the optical image between the pores within the image plane is 400 nm (bottom right ON image). It corresponds to a magnifi cation factor of M ≈ 8. Scale bar, 5 μ m. a,线宽360nm,130nm apart,微米球超级透镜图像,和扫描电镜图像对照,显示其能清洗分辨线。 b、镀导电金膜的AAO样品图像,AAO孔径为50nm,纳米显微镜明显分辨直径50nm孔。微米球透镜将50nm孔的近场光学信息放大了约8倍,光学显微镜图像显示其为400nm。

被广泛报道的--纳米级光学显微镜,是什么东东? - 驰奔 - ---DEMA 驰奔---

Figure 3 | Microsphere nanoscope refl ection mode imaging. ( a )Microsphere superlens refl ection mode imaging of a commercial Blu-ray
DVD disk. The 100- μ m-thick transparent protection layer of the disk was peeled off before using the microsphere ( a = 2.37 μ m). The subdiffraction limited 100 nm lines (top left SEM image) are resolved by the microsphere superlens (top right ON image). ( b ) Refl ection mode imaging of a star structure made on GeSbTe thin fi lm for DVD disk (bottom left SEM image). The complex shape of the star including 90 nm corner was clearly imaged  (bottom right ON image). Scale bar: SEM (500 nm), ON (5 μ m).

 a、微米球透镜反射模式图像,样品商品化blu-rayDVD碟片信道。在使用微米球前,光盘100微米厚的透明保护层被剥离掉。低于远场光学衍射限制的100nm线被微米球透镜分辨开。

b、在DVD碟片的锗锑碲薄膜上制作的星型结构的纳米显微镜反射模式图像,具有90nm尺度的星形角的复杂形状可清晰成像。
以上样品所使用的扫描电镜为钨灯丝SEM, 所有样品都在最高级的油浸远场光学显微镜下试验过,观察不到特征点。
微米球纳米显微镜的成像机制

The imaging mechanism of the microsphere nanoscope . In principle,the imaging resolution and magnification of the microsphere superlenses are fundamentally related to their focus properties  .It is well known that small spheres can generate ‘ photonic nanojets ’ with super-resolution foci  , less well known is that such superresolution foci are only achievable for a narrow window of ( n , q )parameters, where n is the refractive index of the sphere and q is the size parameter defi ned as q = 2 π a / λ , according to Mie theory 16 . Figure 4a shows the calculated super-resolution window for different n and q parameters for spheres immersed in air. Th e y axis was calculated as (focus spot size ? Rayleigh diff raction limit) / radius, which we name as super-resolution strength. For the n = 1.46 spheres used in this study, super-resolution occurs for q < 70, which corresponds to smaller than 9.0- μ m-diameter spheres at a wavelength of λ = 400 nm. From our experiments, it was verified that 10 and 50 μ m spheres are not successful in 100-nm-resolution imaging tests, whereas 3.0 μ m spheres produce clear 50-nm-resolution images as achieved by the 4.74 μ m spheres. We also examined the use of 1 μ m spheres for imaging. It is found that because of the small-view windows of such particles, high-resolution imaging was not successful. Therefore,the limit for 1 μ m sphere is a practical conclusion rather than a theoretical one. The practical size window for n = 1.46 microspheres is recommended as 2 μ m < diameter < 9 μ m for 50-nm-resolution imaging. From Figure 4a , it can also be seen that refractive index has a strong effect on super-resolution foci; with n = 1.8, the size window for super-resolution extends up to q ~ 250, which implies that particles as big as 30 μ m could be used for nanoimaging. This would facilitate the experiments because of wider view windows offered by bigger particles. Moreover, one can see that the superresolution strength is maximized at n = 1.8. When refractive index increases further to n = 2.0, the super-resolution strength reduces and super-resolution window shrinks, making it undesirable to use n > 1.8 high-index materials for nanoimaging in our technique. On the contrary, high-index ( n > 1.8) materials are important for SILs
as their imaging resolution is determined by the refractive index of lens materials because of the solid immersion mechanism. Figure 4b,c compares the | E | 2  intensity distribution for SIL, sphere and particle on surface calculated with the same parameters, that is, n = 1.46, diameter = 4.74 μ m and λ = 600 nm. Here, one important difference between SIL and sphere was demonstrated: a super-resolution focus outside of sphere and a diffraction-limited focus for the same-diameter SIL. Truncating of sphere into SIL causes the loss of super-resolution focus, and diffraction-limited spot of SIL makes it impossible to resolve below 100 nm objects. Super-resolution foci are the key requirement of our technique. With the presence of a substrate, the focus at particle – substrate contact region generally
becomes sharper. Th is is evidenced by our particle on surface calculation ( Fig. 4b,c ). Such effects could enhance the imaging resolution according to the reciprocity principle。

被广泛报道的--纳米级光学显微镜,是什么东东? - 驰奔 - ---DEMA 驰奔---

被广泛报道的--纳米级光学显微镜,是什么东东? - 驰奔 - ---DEMA 驰奔---
SIL  Imax = 90                                      Mie Imax = 107                                       POS      Imax = 153

 Figure 4 | Super-resolution foci and virtual magnification factor analyses.
( a ) Super-resolution strength, defined as (focus spot size ? Rayleigh limit) /radius, as a function of size parameter q for different refractive index particles. The inset shows q up to 300 for n = 1.46. ( b ) The intensity distributions calculated for SIL (left image, height H = a (1 + n ? 1 )), sphere (middle image) and particle on surface(right image) of a 40-nm-thick gold fi lm for the sphere with radius a = 2.37 μ m and refractive index n = 1.46 at the wavelength λ = 600 nm. ( c ) Full width at half maximum of foci for SIL (blue solid), sphere (red dot) and sphere on substrate (green solid). ( d ) Virtual image magnification versus particle size for sphere with n = 1.46 at the wavelength λ = 600 nm.

Discussion

The microsphere nanoscope demonstrated by us has a far-field resolution between λ / 8 and λ / 14 and a magnifi cation between ×4 and × 8 Such resolution and magnifi cation have greatly surpassed those of existing visible wavelength SPP hyperlens 7,8 (resolution λ / 7, magnifi cation ×2.4) and nSILs 11,12 (resolution λ / 2.2, magnifi cation × 2) within the visible spectrum; note that the SiC superlens resolution of λ / 20, as demonstrated in the literature 3 , is not far-fi eld resolution but a near-fi eld resolution in mid-infrared spectrum range.
The microsphere superlenses operate in a virtual imaging mode, and can be easily integrated with an ordinary optical microscope in both transmission and refl ection modes, and work under a standard white-light illumination. From our estimations, it follows that maximal virtual image magnifi cation can be attained with a refractive index n ≈ 1.8. With 5 μ m particles, it should resolve arbitrary structures < 20 nm, making it possible to directly observe viruses and the inside of living cells under white light without the need to excite fl uorescence using proper lasers as in molecular fl uorescence nanoscopy 19 . As a fi nal note, particles in other shapes, such as elliptical particles, could also be considered for below 50 nm imaging as near-field foci strongly depend on particle shape. In conclusion, we have demonstrated that optically transparent microspheres are highperformance optical superlens that could resolve 50 nm objects by near-field virtual imaging under a white-light source illumination. The microsphere nanoscope is robust, economical and is also easy to accommodate diff erent kinds of samples with potential applications for imaging biological objects such as virus, DNA and molecules.

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