散射式太赫兹扫描近场光学显微技术研究

基于散射式近场探测原理,设计并搭建了散射式太赫兹扫描近场光学显微系统(THz s-SNOM),实现了纳米量级空间分辨率的太赫兹近场显微成像测量。该系统以输出频率范围为0.1~0.3THz的太赫兹倍频模块为发射源,通过纳米探针的针尖产生纳米光源与样品相互作用,并将样品表面的倏逝波转化为可在远场测量的辐射波。通过探针逐点扫描样品表面,同时获得了样品表面的形貌图和太赫兹近场显微图。该系统的显微分辨率取决于探针针尖的曲率半径,而与太赫兹波的波长无关。使用该系统测量了金薄膜/硅衬底样品和石墨烯样品的近场显微图,结果表明,近场显微的空间分辨率优于60nm,波长与空间分辨率之比高达λ/26000。     

太赫兹近场光学亚表面检测技术研究

研究了太赫兹散射式扫描近场光学显微镜（Terahertz scattering-type scanning near-field optical microscopy,THz s-SNOM）对亚表面金属微纳结构的显微成像检测。首次采用自主搭建的THz s-SNOM系统对表面覆盖了六方氮化硼薄膜的金微米线进行太赫兹近场显微测量,获得了具有纳米量级空间分辨率和较高对比度的近场显微图。结合全波数值模拟,分析了THz s-SNOM探测亚表面金属微纳结构的空间分辨率、近场散射信号强度和成像对比度。研究表明,THz s-SNOM具有优良的亚表面显微成像检测能力,可应用于微纳电子器件的亚表面结构表征和缺陷检测。     

太赫兹光致力近场显微成像技术及应用研究

设计并搭建了太赫兹光致力显微成像系统(THz PiFM),首次在太赫兹波段实现了近场光力纳米显微成像测量。该系统基于原子力显微镜,利用探针对所受力的灵敏检测能力,通过探测探针与样品之间近场偶极相互作用产生的光场梯度力,实现无探测器的太赫兹近场显微成像。利用该系统,对可见光激发下的单层MoS₂晶粒进行了近场纳米显微成像表征,并分析了晶粒边缘近场光力信号增强的机制。研究结果表明,THz PiFM对二维材料中的载流子具有高灵敏的探测能力。与传统的太赫兹近场显微成像技术相比,THz PiFM无需太赫兹探测器,而且可获得更加优越的空间分辨率和成像信噪比,是一种低成本、高性能的新型太赫兹近场显微成像技术。     

单层MoS2和WS2的太赫兹近场显微成像研究

采用太赫兹散射式扫描近场光学显微镜(THz s-SNOM)研究了化学气相沉积法制备的单层MoS₂和WS₂晶粒的太赫兹近场响应。在没有可见光激发时,未探测到可分辨的太赫兹近场响应,说明晶粒具有较低的掺杂载流子浓度。有可见光激发时,由于光生载流子的太赫兹近场响应,能够测得与晶粒轮廓完全吻合的太赫兹近场显微图。在相同的光激发条件下,MoS₂的太赫兹近场响应强于WS₂,反映了两者之间载流子浓度或迁移率的差异。研究结果表明,THz s-SNOM兼具超高的空间分辨率和对光生载流子的灵敏探测能力,对二维半导体材料和器件光电特性的微观机理研究具有独特的优势。     

扫描近场光学显微镜

本文简介近场光学的基本原理一非辐射场的探测与高分辨率的关系；近场光学显微镜的仪器发展。同时简要介绍近场光学显微镜在超高分辨率光学成象，纳米尺度光学微加工与光刻，高密度磁光存储，近场光谱等领域中的应用。     

近场扫描光学显微镜和光子扫描隧道显微镜

近场扫描光学显微镜和光子扫描隧道显微镜＊王佳（清华大学精密仪器系北京１０００８４）０引言自从８０年代初扫描隧道显微镜ＳＴＭ发明以来，扫描探针显微术ＳＰＭ已经发展成具有十几种类型的系列技术。其中引人注目的是以近场扫描光学显微镜ＮＳＯＭ和光子扫描隧道显微...     

模块化的保偏近场扫描光学显微镜结构设计

采用模块化的设计思想，制成了高质量且简单易用的音又光纤探针模块、模块化的扫描探头、扫描台等，从而研制出高性能，易操作的模块化的保偏近场扫描光学显微镜。     

传统光学显微镜与近场光学显微镜

近场光学显微镜是对于常规光学显微镜的革命。它不用光学透镜成像 ,而用探针的针尖在样品表面上方扫描获得样品表面的信息。分析了传统光学显微镜与近场光学显微镜成像原理的物理本质和两种显微镜系统结构的异同点。介绍了光纤探针的制作方法。重点讨论了近场探测原理、光学隧道效应及非辐射场的性质     

基于半导体的可调谐太赫兹滤波器研究

太赫兹滤波器在通信、传感、成像等领域有着广泛的应用。提出了一个基于半导体材料砷化镓的周期性微结构可调谐太赫兹滤波器,并对半导体材料的电介质特性以及微结构的太赫兹滤波特性进行模拟研究。提出了基于光栅结构的太赫兹滤波器,用CST软件时域有限差分法(FDTD)进行模拟仿真,0.1~5.0THz频段的太赫兹波垂直入射光栅表面,在225~325K范围内可获得工作频率为0.35~1.51 THz,1.16 THz的滤波带宽,同时保持透过率在85%以上,这对太赫兹滤波器的滤波带宽和透过率的提升具有重大意义。     

Coaxial probes for scanning near-field microscopy

This paper deals with the development of coaxial aperture tips integrated in a cantilever probe for combined scanning near-field infrared microscopy and scanning force microscopy. A fabrication process is introduced that allows the batch fabrication of hollow metal aperture tips integrated on a silicon cantilever. To achieve the coaxial tip arrangement a metal rod is deposited inside the hollow tip using the focused ion beam technique. Theoretical calculations with a finite integration code were performed to study the transmission characteristics of coaxial tips in comparison with conventional aperture probes. In addition, the influence of the geometrical design parameters of the coaxial probe on its optical behaviour is investigated.     

Tapping-mode tuning-fork near-field scanning optical microscopy of low power semiconductor lasers

The newly developed inverted tapping-mode tuning-fork near-field scanning optical microscopy (TMTF-NSOM) is used to study the local near-field optical properties of strained AlGaInP/Ga_0.4In_0.6P low power visible multiquantum-well laser diodes. In contrast to shear-force mode NSOM, TMTF-NSOM provides the function to acquire the evanescent wave intensity ratio | I (2ω)|/| I (ω)| image, from which the evanescent wave decay coefficient q can be evaluated for a known tapping amplitude. Moreover, we probe the near-field stimulated emission spectrum, which gives the free-space laser light wavelength λ_o and the index of refraction n _r of the laser diode resonant cavity. Once q , λ_o, and n _r are all measured, we can determine the angle of incidence θ_o of the dominant totally internally reflected waves incident on the front mirror facet of the resonator. Determination of such an angle is very important in modelling the stability of the laser diode resonator.     

Plasmon-coupled tip-enhanced near-field optical microscopy

Near the cut‐off radius of a guided waveguide mode of a metal‐coated glass fibre tip it is possible to couple radiation to surface plasmons propagating on the outside surface of the metal coating. These surface plasmons converge toward the apex of the tip and interfere constructively for particular polarization states of the initial waveguide mode. Calculations show that a radially polarized waveguide mode can create a strong field enhancement localized at the apex of the tip. The highly localized enhanced field forms a nanoscale optical near‐field source.     

Femtosecond near-field scanning optical microscopy study of molecular thin films

A near-field scanning optical microscope has been combined with a two-colour time-resolved pump-probe measurement system. It has a noise-equivalent transmittance change of 5.0 × 10⁻⁵ for a probe pulse with an intensity of 30 nW. The system has been used for evaluating molecular thin films that have a domain structure, particularly for observing a gate action of the single domains. The results include key features to understand an origin of the domains and suggest that the film composition is uniform over a distance of several micrometres.     

Single molecule mapping of the optical field distribution of probes for near-field microscopy

The most difficult task in near-field scanning optical microscopy (NSOM) is to make a high quality subwavelength aperture probe. Recently, we have developed high definition NSOM probes by focused ion beam (FIB) milling. These probes have a higher brightness, better polarization characteristics, better aperture definition and a flatter end face than conventional NSOM probes. We have determined the quality of these probes in four independent ways: by FIB imaging and by shear-force microscopy (both providing geometrical information), by far-field optical measurements (yielding throughput and polarization characteristics), and ultimately by single molecule imaging in the near-field. In this paper, we report on a new method using shear-force microscopy to study the size of the aperture and the end face of the probe (with a roughness smaller than 1.5 nm). More importantly, we demonstrate the use of single molecules to measure the full three-dimensional optical near-field distribution of the probe with molecular spatial resolution. The single molecule images exhibit various intensity patterns, varying from circular and elliptical to double arc and ring structures, which depend on the orientation of the molecules with respect to the probe. The optical resolution in the measurements is not determined by the size of the aperture, but by the high optical field gradients at the rims of the aperture. With a 70 nm aperture probe, we obtain fluorescence field patterns with 45 nm FWHM. Clearly, this unprecedented near-field optical resolution constitutes an order of magnitude improvement over far-field methods like confocal microscopy.