基于半导体纳米线/锥形微光纤探针的被动式近场光学扫描成像

本文结合近场扫描结构和纳米线-微光纤耦合技术,提出了一种基于硫化镉纳米线/锥形微光纤探针结构的被动近场光学扫描成像系统.该系统采用被动式纳米探针,保留了纳米探针对样品表面反射光的强约束优势.其理论收集效率为4.65‰,相比于传统的金属镀膜近场探针收集效率提高了一个数量级,可有效地提高扫描探针对样品形貌信息的检测能力;而后通过硫化镉纳米线与微光纤之间高效的倏逝场耦合,将检测的光强信号传输到远场进行光电探测,最终实现对目标样品形貌的分析成像,其样品宽度测量误差在7.28%以内.该系统不需要外部激发光路,利用显微镜自身光源进行远场照明,被动扫描探针仅作为样品表面反射光的被动收集系统.本文基于半导体纳米线/锥形微光纤探针的被动式近场光学扫描成像方案,可有效地降低探针的制备难度和目标光场的检测难度,简化扫描成像的结构,为近场光学扫描显微系统之后的发展提供新的思路.

Passive near-field optical scanning imaging based on semiconductor nanowire/tapered microfiber probe

In this paper,we propose a passive near-field scanning imaging system by using the structure of cadmium sulfide(CdS)nanowire/tapered microfiber probe,which combines the near-field scanning structure and the nanowire/microfiber coupling technology.In the passive near-field scanning imaging system,a passive nanoprobe is adopted to detect the intensity change of the reflected light field on the sample surface,which not only retains the advantage of the nanoprobe for the strong restriction of the reflected light on the sample surface,but also reduces the interference of strong excitation light during detection.Through the high efficiently evanescent field coupling between the CdS nanowire and the tapered microfiber,the collected light signal is transmitted to the photodetector in the far field,and finally the imaging of the target sample morphology can be realized.At first,the light field model of the nanowire/tapered microfiber probe structure is verified by the finite element analysis method.The calculated collection efficiency from the sample to the probe is about 4.65‰and the transmission efficiency from the nanowire to the tapered microfiber is about 74.47%.The collection efficiency is improved by an order of magnitude compared with traditional metal-coated near-field probe.In the experiments,a scanning step of 20 nm and a probe-sample distance of 230 nm are selected.The nanowire/tapered microfiber probe and traditional tapered fiber probe are both used to measure the widths of different CdSe nanoribbons samples,and the atomic force microscopy measurement is used as the benchmark to calculate their measurement error,which is increased about 3 times.By changing the angleθbetween the probe and the sample,it is found that the resolution obtained using the designed nanowire/microfiber probe is always higher than only using the tapered microfiber probe.Comparing with the tapered microfiber probe scheme,the measurement error is reduced to a value less than 7.2%.In addition,compared with the active luminescence probe scheme,this passive near-field scanning scheme reduces the preparation complexity of the optical probe and the detection structure complexity of the optical system.The large microscopic illumination area can avoid the influence of the small laser spot size on imaging,and the imaging range is determined only by the travel distance of the linear stage.Therefore,our work may provide an attractive approach for developing new near-field scanning microscopy systems in the future.