The strong localization of surface plasmon polariton on a metal-coated tip of optical fiber

It is shown that during the propagation of surface plasmon polariton (SPP) on a metal-coated tip of an optical fiber its wavelength essentially decreases and wave fields anomalously increase. Dependence of a degree of localization of SPP on sharpness of the structure and width of the metal layer is defined. The received results can be used to increase the resolution of scanning optical microscope.     

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。     

Electrical detection of β-amyloid (1-40) using scanning tunneling microscopy

Numerous studies have shown that the presence of β-amyloid (1-40) in cerebrospinal fluid can be used as a potential biomarker for Alzheimer's disease. Identifying biomarkers for Alzheimer's disease is highly important because these biomarkers could be used to establish the diagnosis before the disease reaches clinical severity. In this study, a vertically configured electrical detection system associated with scanning tunneling microscopy (STM) was used to characterize antigen–antibody binding interactions. The proposed technique can be easily utilized to construct a multiple measurement system in a protein chip. The immunocomplexes used in the model protein comprise β-amyloid (1-40), corresponding antibody fragments, and gold nanoparticle–antibody conjugates. The electrical tunneling current between the STM tip and these complexes exhibited a peak-like pulse, where the frequency of these pulses was dependent on the surface density of bound complexes. Hence, a quantitative measurement of β-amyloid concentration from a periodogram analysis of peak frequency was successfully achieved at concentrations as low as 1 fg/mL.     

Imaging of optical disc using reflection-mode scattering-type scanning near-field optical microscopy

A phase-change optical disc was observed using a reflection-mode scattering-type scanning near-field optical microscope (RS-SNOM). In an a.c.-mode SNOM image, the 1.2 μm × 0.6 μm recording marks were successfully observed although the data were recorded on the groove. In contrast, no recording marks could be resolved in a d.c.-mode SNOM image. These results are in good agreement with those from a numerical simulation using the finite difference time domain method. The resolution was better than 100 nm with a.c.-mode SNOM operation and the results indicate that recording marks in phase-change optical media can be directly observed with the RS-SNOM.     

散射型近场扫描光学显微镜的探针振动参数优化研究

基于原子力显微镜平台设计了可见-近红外波段的散射型近场扫描光学显微镜,通过理论模型计算和实验测量,分析了散射探针振动的调制振幅和扫描反馈幅值对近场信号的影响。研究表明:与探针针尖尺寸相近的调制振幅有利于抑制背景散射噪声及优化近场信号的信噪比;当探针扫描反馈幅值与自由空间调制振幅之比大于90%时,可基本消除探针扫描过程中非简谐振动对近场成像测量的影响。     

Femtosecond near-field scanning optical microscopy

We have developed an instrument for optically measuring carrier dynamics in thin-film materials with ≈150 nm lateral resolution, ≈250 fs temporal resolution and high sensitivity. This is accomplished by combining an ultrafast pump–probe laser spectroscopic technique with a near-field scanning optical microscope. A diffraction-limited pump and near-field probe configuration is used, with a novel detection system that allows for either two-colour or degenerate pump and probe photon energies, permitting greater measurement flexibility than that reported in earlier published work. The capabilities of this instrument are proven through near-field degenerate pump–probe studies of carrier dynamics in GaAs/AlGaAs single quantum well samples locally patterned by focused ion beam (FIB) implantation. We find that lateral carrier diffusion across the nanometre-scale FIB pattern plays a significant role in the decay of the excited carriers within ≈1 μm of the implanted stripes, an effect which could not have been resolved with a far-field system.     

Near-field reflection backscattering apertureless optical microscopy: application to spectroscopy experiments on opaque samples, comparison between lock-in and digital photon counting detection techniques

An apertureless scanning near-field optical microscope (ASNOM) in reflection backscattering configuration is designed to conduct spectroscopic experiments on opaque samples constituted of latex beads. The ASNOM proposed takes advantage of the depth-discrimination properties of confocal microscopes to efficiently extract the near-field optical signal. Given their importance in a spectroscopic experiment, we systematically compare the lock-in and synchronous photon counting detection methods. Some results of Rayleigh's scattering in the near field of the test samples are used to illustrate the possibilities of this technique for reflection backscattering spectroscopy.     

Probe design optimization for a high-resolution scattering-type scanning near-field optical microscope

The scattering-type scanning near-field optical microscope (SNOM) has a probe with a sharp tip for use in high resolution imaging. As sharp a tip as possible is generally considered ideal for the observations, but actually, a sharp tip does not always provide a high resolution SNOM image. We numerically examined the scattering property of the SNOM probe by the three dimensional finite difference time domain method. In this paper, we show the criterion for the ideal scattering probe which satisfies the simple relation between radius and taper angle of the tip.     

Shape dependence of the capacitance of scanning capacitance microscope probes

The capacitance of approximately conical scanning capacitance microscope probes placed perpendicularly over a conducting plane has been modelled using the finite element method. The dependence on tip/surface distance, radius of curvature of the tip apex, cone angle and height has been analysed. Both shielded and unshielded probes have been considered. The fits of obtained dependences have been combined into an analytic approximation of the capacitance as a function of tip/surface distance, radius of curvature, cone angle and height. The results can be used to estimation of stray capacitance, achievable lateral resolution and contrast.     

Electron beam confinement and image contrast enhancement in near field emission scanning electron microscopy

In conventional scanning electron microscopy (SEM), the lateral resolution is limited by the electron beam diameter impinging on the specimen surface. Near field emission scanning electron microscopy (NFESEM) provides a simple means of overcoming this limit; however, the most suitable field emitter remains to be determined. NFESEM has been used in this work to investigate the W (1 1 0) surface with single-crystal tungsten tips of (3 1 0), (1 1 1), and (1 0 0)-orientations. The topographic images generated from both the electron intensity variations and the field emission current indicate higher resolution capabilities with decreasing tip work function than with polycrystalline tungsten tips. The confinement of the electron beam transcends the resolution limitations of the geometrical models, which are determined by the minimum beam width.     

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.     

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.     

A single gold particle as a probe for apertureless scanning near-field optical microscopy

We report on the fabrication, characterization and application of a probe consisting of a single gold nanoparticle for apertureless scanning near-field optical microscopy. Particles with diameters of 100 nm have been successfully and reproducibly mounted at the end of sharp glass fibre tips. We present the first optical images taken with such a probe. We have also recorded plasmon resonances of gold particles and discuss schemes for exploiting the wavelength dependence of their scattering cross-section for a novel form of apertureless scanning near-field optical microscopy.     

Towards better scanning near-field optical microscopy probes — progress and new developments

Several approaches are described with the aim of producing near-field optical probes with improved properties. Focused ion beam milling allows the fabrication of small apertures in a controlled fashion, resulting in probes with excellent polarization properties and increased transmission. Microfabrication processes are described that allow the production of apertures of 30–50 nm, facilitating the mass-fabrication of apertured tip structures that can be used in a combined force/near-field optical microscope. Finally, possible future developments are outlined.     

Fluorescence in situ hybridization on human metaphase chromosomes detected by near-field scanning optical microscopy

Fluorescence in situ hybridization on human metaphase chromosomes is detected by near-field scanning optical microscopy. This combination of cytochemical and scanning probe techniques enables the localization and identification of several fluorescently labelled genomic DNA fragments on a single chromosome with an unprecedented resolution. Three nucleic acid probes are used: pUC1. 77. p1–79 and the plasmid probe α-spectrin. The hybridization signals are very well resolved in the near-field fluorescence images, while the exact location of the probes can be correlated accurately with the chromosome topography as afforded by the shear force image.     

Optical microcantilever consisting of channel waveguide for scanning near-field optical microscopy controlled by atomic force

We develop a novel optical microcantilever for scanning near-field optical microscopy controlled by atomic force mode (SNOM/AFM). The optical microcantilever has the bent channel waveguide, the corner of which acts as aperture with a large tip angle. The resonance frequency of the optical microcantilever is 9 kHz, and the spring constant is estimated to be 0.59 N/m. The optical microcantilever can be operated in contact mode of SNOM/AFM and we obtain the optical resolution of about 200 nm, which is as same size as the diameter of aperture. We confirm that the throughput of optical microcantilever with an aperture of 170 nm diameter would be improved to be more than 10⁻⁵.