Silicon is a high refractive index material. Consequently, silicon nanowires (SiNWs) with diameters on the order of the wavelengths of visible light show strong resonant field enhancement of the incident light, so this type of nanomaterial is a good candidate for all kinds of photonic devices. Surprisingly enough, a thorough experimental and theoretical analysis of both the polarization dependence of the absorption and the scattering behavior of individual SiNWs under defined illumination has not been presented yet. Here, the present paper will contribute by showing optical properties such as scattering and absorption of individual SiNWs experimentally in an optical microscope using bright- and dark-field illumination modes as well as in analytical Mie calculations. Experimental and calculation results are in good agreement, and both reveal a strong correlation of the optical properties of individual SiNWs to their diameters. This finding supports the notion that SiNWs can be used in photonic applications such as for photovoltaics or optical sensors.

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Electrical and optical properties of semiconducting nanowires (NWs) strongly depend on their diameters. Therefore, a precise knowledge of their diameters is essential for any kind of device integration. Here, we present an optical method based on dark field optical microscopy to easily determine the diameters of individual NWs with an accuracy of a few nanometers and thus a relative error of less than 10%. The underlying physical principle of this method is that strong Mie resonances dominate the optical scattering spectra of most semiconducting NWs and can thus be exploited. The feasibility of this method is demonstrated using GaAs NWs but it should be applicable to most types of semiconducting NWs as well. Dark field optical microscopy shows that even slight tapering of the NWs, i.e. diameter variations of a few nanometers, can be detected by a visible color change. Abrupt diameter changes of a few nanometers, as they occur for example when growth conditions vary, can be determined as well. In addition a profound analysis of the elastic scattering properties of individual GaAs NWs is presented theoretically using Mie calculations as well as experimentally by dark field microscopy. This method has the advantage that no vacuum technique is needed, a fast and reliable analysis is possible based on cheap standard hardware.

Driven by the demand for ongoing integration and increased complexity of today's microelectronic circuits, smaller and smaller structures need to be fabricated with a high throughput. In contrast to serial nanofabrication techniques, based, e.g., on electron beam or scanning probe methods, optical methods allow a parallel approach and thus a high throughput. However, they rarely reach the desired resolution. One example is plasmon lithography, which is limited by the utilized plasmonic metal structures. Here we show a new approach extending plasmonic lithography with the potential for a highly parallel nanofabrication with a higher level of complexity based on nanoantenna effects combined with molecular nanowires. Thereby femtosecond laser pulse light is converted by Ag nanoparticles into a high plasmonic excitation guided along attached DNA structures. An underlying poly(methyl methacrylate) (PMMA) layer acting as an electron-sensitive resist is so structured along the former DNA position. This apparently DNA-guided effect leads to nanometer grooves reaching even micrometers away from the excited nanoparticle, representing a novel effect of long-range excitation transfer along DNA nanowires.

Certain metal nanoparticles exhibit the effect of localized surface plasmon resonance when interacting with light, based on collective oscillations of their conduction electrons. The interaction of this effect with molecules is of great interest for a variety of research disciplines, both in optics and in the life sciences. This paper attempts to describe and structure this emerging field of molecular plasmonics, situated between the molecular world and plasmonic effects in metal nanostructures, and demonstrates the potential of these developments for a variety of applications.

Dawn of nanotechnology: the immersion ultramicroscope was patented a century ago. When an analyte was examined with an antique instrument and with state-of-the-art technology, the historic assumptions were confirmed: the size and shape of the nanoparticles are in the same range as that described 100 years ago. The spectra of the Tyndall cones caused by the shape of the nanoparticles were also described correctly-long before electron microscopy was able to image single nanoparticles.

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The scattering of single nanoparticles (NPs) is used in biosensing as molecular label or as a sensor transducer, indicating the adsorption of molecules on the nanoparticles. Currently, a dark-field microscopy setup is used to separate the scattered light signal of the NP from background noise, requiring precise optical elements and cumbersome use of immersion oil. Here we present an alternative, simpler method of suppressing the background noise by using subwavelength apertures. The nanoparticle spectroscopy is carried out in a transmission configuration with an additional chromium mask with apertures that is placed in front of the nanoparticles. Because the detected transmitted light passing through the aperture is spatially restricted to the comparable size of a single metallic nanoparticle, a nanoparticle placed into the aperture sufficiently changes the spectral properties of the transmitted light. Initially in this work the size of the apertures for an optimal detection of the transmitted signal is investigated. It is followed by the measurement of transmitted light through the aperture in the presence of a varying number of nanoparticles. These spectroscopic results correlated with topological characterization techniques (scanning electron microscopy, atomic force microscopy) show that the number of the nanoparticles can be determined based on the spectral characteristics. Furthermore, a spectral shift of scattered light from metal nanoparticle upon binding molecules is observed, which can be utilized as a sensoric effect. This is demonstrated by binding DNA molecules to the nanoparticles in the apertures and measuring the change of the transmitted light. The experimental measurements are supported by theoretical calculations. The transmission spectra through subwavelength apertures with and without nanoparticles were simulated and qualitatively confirmed the experimental spectra. The results of this work represent a proof-of-principle toward biosensors based on single metallic nanoparticle utilizing a novel readout (light transmission through subwavelength apertures) without the need for a dark-field microscopy configuration.