NSOM近场光学

1、NSOM 近场光学 界面和倏逝场透射和反射系数近场光学近场光学的历史1928 AD E. H. Synge ( England )1973 AD Ash & Nichols 微波实验证实 1956 AD OKeefe 相关理论的提出1982 AD G. Binning & H. Rohrer 第一步STM诞生1984 AD D. W. Phol 等人 近场光学技术与STM结合1989 AD R. C. Reddick 等人 发展具有光学回馈的NSOM且开 启了以腐蚀方法制作探针1992 AD Eric Betzig 近场光学技术与AFM的结合近场显微术 The near fie

2、ld decays exponentially with distance The tip should be kept at a controllede distance from the sample surface Feed back mechanism: shear force (similar to AFM tapping mode) Feedback detection: quartz oscillator (STM current is not suitable for biological samples; optical methods are disturbing the

3、optical response).xyz piezoFeedbackImpedance detectorElectrodesPiezo actuatorAperture SNOMAperture SNOMIlluminationCollectionIlluminationcollectionReflectioncollectionTransmissionilluminationTransmission collectionOperational modes Typical set upAperture SNOMLaserPol. controlfeedbackcontrolxyzScanne

4、rDetectorTopographic imagenf optical imageInvertedoptical microscopeOptical fiberMonochromator SNOM tipsAperture SNOMpullingbreakingheatingHeating and pulling methodTurner etching methodHydrofluoric acidChemical etchingAluminum vaporGlassAl coatingOptical fiber SNOM tips Calculation of the distribut

5、ion of electric field as a function of the tip geometryAperture SNOMSource: InAs QdotPoint like source l/40 below the surface SNOM tips - pullingAperture SNOMLight propagation SNOM tips - etchingAperture SNOMLight propagationHoles are dug by various methods:The best results are obtained by FIB NSOM

6、应用的优点 与传统光学显微镜比较衍射极限的突破 大幅降低设备成本理想透镜可分辨的最小距离 D D = 0.61NA：入射光波长NA：透镜的数值孔径与电子扫描式显微镜 ( AFM、STM)比较非破坏性测量 可侦测到真实的表面 ( Real Surface Measurement )样品不需繁复的制备手续无需在真空下检测具有其他光学性质的优点应 用近场光学原理除了 应用于近场光学显微镜、作为纳米尺寸的局部光学强度与材料的光学特性等测量用外，由于此技术同时具有纳米尺寸加工与曝光的能力，故还可用于制作单电子晶体管、量子阱等纳米元件，以及应用于更高密度的存储器上。 optical quantum cor

7、ralAperture SNOMThe experiment:Testing the subwavelkenght modulation induced on the local density of states of the optical modes by the fabrication of nanometric opticla corralsSubstrate ITOModulators 100nm100nm50nm gold particles deposited by e-beam lithographyTo test the real LDOS the tip should a

8、ct as a perfetct dipole at a nanometric distance from the surface.Real tips always pertirb the LDOS and what is measured is the combined LDOS of the sample and the tip!optical quantum corralLight Polarization controlElliptical mirros that selects only the near field radiation (propagating radiation is not allowed in the “forbidden light region with qqcThe signal is 0 only closo to the sampleoptical quantum corralTeorical optical LDOS in x, y and z directionoptical quantum corralNear field results in trasmission.Best results obtained with a gold coated tip without ape