It is a general belief in apertureless near-field microscopy that the so-calledp-polarization configuration, where the incident light is polarized parallel to the axis of the probe, is advantageous to its counterpart, thes-polarization configuration, where the incident light is polarized perpendicular to the probe axis. While this is true for most samples under common near-field experimental conditions, there are samples which respond better to thes-polarization configuration due to their orientations. Indeed, there have been several reports that have discussed such samples. This leads us to an important requirement that the near-field experimental setup should be equipped with proper sensitivity for measurements withs-polarization configuration. This requires not only creation of effective s-polarized illumination at the near-field probe, but also proper enhancement of s-polarized light by the probe. In this paper, we have examined thes-polarization enhancement sensitivity of near-field probes by measuring and evaluating the near-field Rayleigh scattering images constructed by a variety of probes. We found that thes-polarization enhancement sensitivity strongly depends on the sharpness of the apex of near-field probes. We have discussed the efficient value of probe sharpness by considering a balance between the enhancement and the spatial resolution, both of which are essential requirements of apertureless near-field microscopy.

Plasmonic nanolens, a 3-dimensional tapered arrangement of metallic nanorod chains, holds a great promise as a new plasmonics-based optical nano-imaging technique. While multiple nanorod chains can transfer the near-field signal originating from a sample to an image at a distance larger than a micro-meter, where each nanorod chain contributes in forming one pixel in the image, the tapered arrangement of the nanorod chains with a certain taper angle allows image magnification. We experimentally demonstrate the feature of image formation and magnification in a nanolens by fabricating a tapered arrangement of two silver nanorod chains, which were separated by a distance smaller than the diffraction limit at one end and larger than the diffraction limit at the other end. We placed two nano-sized optical sources of quantum dots near the first ends of the chains, which served as two subwavelength objects. In the optical measurement, we demonstrated that the unresolved subwavelength optical sources could be imaged at the other ends of the chains and were well resolved in accordance with the magnification feature of a nanolens. This verification is an experimental proof of the image magnification, and an important step toward the realization of plasmonic nanolens.

Plasmonics-based nanoimaging techniques have recently attracted significant attention owing to their ability to confine light to the nanoscale for super-resolution imaging. A recent report has theoretically predicted that a plasmonic nanolens, a well-designed array of metallic nanorod chains, can produce a magnified color image of subwavelength objects through a plasmonic transfer of near-field light as a new class of nanoimaging technique. In this study, we fabricate a gold-nanorod chain through a self-assembly method to experimentally validate this concept, and observe the plasmonic transfer of near-field light from subwavelength objects, which demonstrates the significant potential of plasmonic nanolens for super-resolution imaging.

The hydrogenation of carbobenzoxy phenylalanine was investigated in order to better understand the influence of mass transfer effects in four-phase fixed-bed reactor systems. In this reaction, the carbobenzoxy phenylalanine is dissolved in an organic solvent and is reacted with a gas in the presence of a hydrophilic catalyst (Pd/Al2O3). An aqueous phase is also required to dissolve the reaction product, leading to a four-phase gas–liquid–liquid–solid system. Results indicate that higher liquid flow rates lead to faster rates of reaction due to improved contact efficiency between the organic phase and catalyst. Similar performance was observed through experiment and modeling in two fixed-bed reactor configurations (trickle-bed reactor and gas–liquid cocurrent upflow reactor) at higher liquid flow rates.

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