Near‐field optical microscopy based on microfabricated probes

We demonstrate high resolution imaging with microfabricated, cantilevered probes, consisting of solid quartz tips on silicon levers. The tips are covered by a 60‐nm thick layer of aluminium, which appears to be closed at the apex when investigated by transmission electron microscopy. An instrument specifically built for cantilever probes was used to record images of latex bead projection patterns in transmission as well as single molecule fluorescence. All images were recorded in constant height mode and show optical resolutions down to 32 nm.     

Nanoscopic observation of a gold nanoparticle-conjugated protein using near-field scanning optical microscopy

This study describes a single gold nanoparticle (AuNP)-based observation of biomolecular interaction using a near-field scanning microscope (NSOM) in transmission mode. To observe streptavidin molecules, a glass surface was first patterned with a micro-scale line of (3-aminopropyl)trimethoxysilane (APTMS) by micro-contact printing (μCP) with a subsequent reaction of N-hydroxysuccinimide (NHS)-biotin. The AuNP-conjugated streptavidin was then applied to the biotin-modified glass surface and NSOM was employed to detect the resulting specific interaction between streptavidin and biotin on the glass surface. Using the optical and topological images generated from the NSOM analysis, the interaction could be observed at the nanoscopic scale. This study demonstrates that the NSOM is a powerful tool for the detection of protein interactions at the nanoscopic level when the protein is conjugated with AuNPs.     

Non-optically probing near-field microscopy with illumination of total internal reflection

We have developed a non-optically probing near-field microscope with illumination of total internal reflection. Because the illumination light does not pass through the specimens, it is possible to observe thick specimens or highly absorptive materials. It reduces the background noise because the decay length of the evanescent wave is a few hundred nanometres. We found that although in the total internal reflection illumination system the light passed through the photosensitive film and illuminated the specimen, it did not affect the photosensitive film severely and did not limit the resolution. The imaging properties of reflection illumination and transmission illumination are analysed using a finite-differential time domain method.     

一种基于剪切力的距离控制方法在扫描近场光学显微镜中的应用

介绍了扫描近场光学显微镜中基于剪切力的样品、探针间距离控制的方法。当受振动激励的光纤探针由远处逐渐接近样品表面时,样品与针尖间的剪切力使针尖的振动振幅减小,通过检测探针振幅的变化从而控制针尖与样品间的距离。此种方法可以方便地将光纤探针导入工作区域内并在扫描过程中保持适当的高度。我们测量了探针系统的幅频特性和力曲线,并用该方法获得4μm×4μm的范围内光盘表面的形貌信息。     

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.     

An evanescent-field optical microscope

The classic diffraction limit of resolution in optical microscopy (～γ/2) can be overcome by detecting the diffracted field of a submicrometre-size probe in its near field. The present stage of this so-called scanning near-field optical microscopy (SNOM) is reviewed. An evanescent-field optical microscope (EFOM) is presented in which the near-field regime is provided by the exponentially decaying evanescent field caused by total internal reflection at a refractive-index transition. A sample placed in this field causes a spatial variation of the evanescent field which is characteristic for the dielectric and topographic properties of the sample. The evanescent field is frustrated by a dielectric probe and thus converted into a radiative field. In our case the probe consists either of an etched optical fibre or of a highly sharpened diamond tip. The probe is scanned over the sample surface with nanometre precision using a piezo-electric positioner. The distance between probe and sample is controlled by a feedback on the detected optical signal. The resolution of the microscope is determined by both the gradient of the evanescent field and the sharpness of the tip. Details of the experimental set-up are discussed. The coupling of the evanescent field to the submicrometre probe as a function of probe-sample distance, angle of incidence and polarization has been characterized quantitatively. The observed coupling is generally in agreement with presented theoretical calculations. Microscopy has been performed on a regular latex sphere structure, which clearly demonstrates the capacity of the evanescent-field optical microscope for nanometre-scale optical imaging. Resolution is typically 100 nm laterally and 10 nm vertically. The technique is promising for biological applications, especially if combined with optical spectroscopy.     

Autocorrelation spectroscopy on single ultrathin layers of CdSe/ZnSe: hints for a non-thermal distribution of excitons in quantum islands

Autocorrelation spectroscopy on the basis of thousands of individual near-field photoluminescence spectra of single ultrathin CdSe layers at low temperatures exhibits a strong positive correlation peak around 18 meV energy with a width of 5 meV. Using simulations and experiments as a function of temperature and laser intensity, we can exclude interpretations along the lines of biexcitons or phonon sidebands. We attribute this feature to the splitting of ground state and an excited state in individual quantum islands. This interpretation implies that the potential minima are rather uniform in size and that the distribution of excitons is nonthermal.     

扫描近场光学显微镜对细胞超微结构的研究

扫描近场光学显微镜(SNOM)突破了光学显微镜的衍射极限,在细胞研究中具有高灵敏性、无侵入性等优点,已经广泛的应用于生物学研究中。本文综述了SNOM在细胞膜、细胞器、细胞精细结构和单分子探测等领域的研究进展,介绍了扫描近场光学显微镜结合量子点的方法,并对其应用前景做了展望,对其面临困难做了概述。作为一种研究工具,SNOM在生物领域的应用还远远不足。     

SNOM/SFM结合的近场光学探针

介绍了近年来近场光学探针技术的进展，特别是可与扫描力显徽镜结合的探针制备技术。     

Comparison of convergent beam electron diffraction and geometric phase analysis for strain measurement in a strained silicon device

Convergent beam electron diffraction and geometric phase analysis were used to measure strain in the gate channel of a p-type strained silicon metal-oxide-semiconductor field-effect transistor. These measurements were made on exactly the same transmission electron microscopy specimen allowing for direct comparison of the relative advantages of each technique. The trends in the strain values show good agreement in both the [110] and [001] directions, but the absolute strain values are offset from each other. This difference in the absolute strain measured using the two techniques is attributed to the way the reference strain is defined for each.