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Light propagation in Photonic integrated circuits (PICs), which can nowadays involve complex systems of light-guiding structures, is measured with different approaches(Nuzhdin et al., 2020, Lončar et al., 2002, Hopman et al., 2007, Morichetti et al., 2014, Sapienza et al., 2012, Vesseur et al., 2007). An interferometric polarization-sensitive measurement of the evanescent fields of these structures provides insight in the performance of the circuit detects possible malfunction with sub-wavelength precision(Engelen et al., 2007, Gersen et al., 2005, Barwick et al., 2009). We demonstrate a Near-field scanning optical microscopy (NSOM) measurement on coupled ring resonators that shows how the guided modes evolve as they propagate across the optical chip. Analysis of the measurements provides information about intensity distribution of the two polarization components (TE and TM) and their spatial confinement. The data validates our methodology and opens new possibilities for analysis of signal propagation in prototyping and optimization of integrated optical systems. Direct observation of polarization state of the guided modes allows for clear understanding of mode conversion in coupling systems.

Plasmonic nanoantennas are pushing the limits of optical imaging resolution capabilities in near-field scanning optical microscopy (NSOM). Accordingly, these techniques are driving the basic understanding of photonic and optoelectronic nanoscale devices with applications in sensing, energy conversion, solid-state lighting, and information technology. Imaging the localized surface plasmon resonance (LSPR) at the nanoscale is a key to understanding the optical responses of a given tip geometry in order to engineer better plasmonic nanoantennas for near-field experiments. In recent years the advancement of focused ion beam technology provides the ability to directly modify plasmonic structures with nanometer resolution. Also, scanning transmission electron microscopy (STEM) with electron energy loss spectroscopy (EELS) is an established technique allowing imaging of LSPR. Specifically, the combination of these two techniques provides spectrally sensitive two-dimensional (2D) image information to better visualize and understand LSPR on the nanometer scale. This can be combined with electron tomography to provide the three-dimensional LSPR distribution. Here we demonstrate the fabrication of Au nanopyramids using helium ion microscopy, and analyze the LSPR in 3D reconstructions produced by total variation (TV)-norm minimization of a set of 2D STEM-EELS maps. Additionally, a boundary element simulation method was used to verify the experimentally observed nanopyramid LSPR modes. Finally, we show that the point-spread-functions (PSF) of LSPR mode hot spots in nanopyramids differ to local electric-field enhancement under optical excitation making direct comparison to NSOM experimental resolution difficult. However, the STEM-EELS results show how LSPR modes are influenced by the tip characteristics, which can inform the development of new nanoantenna designs.

Highly evanescent waveguides with a subwavelength core thickness present a promising lab-on-chip solution for generating nanovolume trapping sites using overlapping evanescent fields. In this work, we experimentally studied Si3N4 waveguides whose sub-wavelength cross-sections and high aspect ratios support fundamental and higher order modes at a single excitation wavelength. Due to differing modal effective indices, these co-propagating modes interfere and generate beating patterns with significant evanescent field intensity. Using near-field scanning optical microscopy (NSOM), we map the structure of these beating modes in three dimensions. Our results demonstrate the potential of NSOM to optimize waveguide design for complex field trapping devices. By reducing the in-plane width, the population of competing modes decreases, resulting in a simplified spectrum of beating modes, such that waveguides with a width of 650 nm support three modes with two observed beats. Our results demonstrate the potential of NSOM to optimize waveguide design for complex field trapping devices.

This article provides a careful comparison between the electric and mechanical excitation of a tuning fork for shear force feedback in scanning probe microscopy, an analysis not found in present literature. A setup is designed and demonstrated for robust signal and noise measurements at comparable levels of physical movement of the probe. Two different signal amplification methods, combined with two excitation ways provide three possible configurations. For each method a quantitative analysis, supported by analytical elaboration and numerical simulations, is provided. Finally, it is shown that in practical circumstances electric excitation followed by detection with a transimpedance amplifier provides the best result. • Shear force feedback provides height feedback in scanning probe microscopy. • Quartz tuning forks outfitted with sharp probe suit purpose of shear force detection. • Sub-micrometer movement of a tuning fork induces interaction between tip and sample. • Possible tuning fork excitation and signal detection methods impact measurement. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate simultaneous AFM/NSOM using a dual-tip normal tuning-fork based scanning probe microscope. By scanning two SPM probes simultaneously, one dedicated for AFM with a standard tip diameter of 20 nm, and the second having a 150 nm aperture NSOM fiber with 200 nm thick gold coating, we combine the benefits of ∼20 nm spatial resolution from the AFM tip with the spectral information of a near-field optical probe. The combination of simultaneous dual-tip scanning enables us to decouple the requirements for high resolution topography and probe functionality. Our method represents a marked shift from previous applications of multi-probe SPM where essentially a pump-probe methodology is implemented in which one tip scans the area around the second. As a model system, we apply dual-tip AFM/NSOM scanning to a sample of spin-cast nano-clustered Lumogen dyes, which show remarkable brightness and photochemical stability. We observe morphology features with a resolution of 20 nm, and a near-field optical resolution of 150 nm, validating our approach.

The size of the V-defects in the GaN/InGaN-based quantum wells blue light-emitting diode (LED) was intentionally modified from 50 nm to 300 nm. High resolution photoluminescence and electroluminescence of a single large V-defect were investigated by near-field scanning optical microscopy. The current distribution along the {10-11} facets of the large defect was measured by conductive atomic force microscopy. Nearly 20 times the current injection and dominant emission from bottom quantum wells were found in the V-defect compared to its vicinity. Such enhanced current injection into the bottom part of quantum wells through V-defect results in higher light output power. Reduced external quantum efficiency droops were achieved due to more uniform carrier distribution. The un-encapsulated fabricated chip shows light output power of 172.5 mW and 201.7 mW at 400 mA, and external quantum efficiency drop of 22.3% and 15.4% for the sample without and with large V-defects, respectively. Modified V-defects provide a simple and effective approach to suppress the efficiency droop problem that occurs at high current injection, while improving overall quantum efficiency.

Subwavelength confined waveguiding is experimentally demonstrated with high refractive index dielectric nanoparticles with photon energy propagation at distances beyond 500 μm. These particles have naturally occurring electric and magnetic dipole resonances. When they are placed in a 1D chain, the magnetic resonances of adjacent elements couple to each other, providing a means to transport energy at visible or NIR wavelengths in a confined mode. Chains of nanoparticles made of silicon were fabricated and guided waves were measured with near-field scanning optical microscopy. Propagation loss is quantified at 34 dB/mm for 720 nm and 5.5 dB/mm for 960 nm wavelengths with 150 and 220 nm diameter particles, respectively. Simulations confirm the unique properties of this waveguiding in comparison with photonic crystals. The resonant nature of the waveguide lays a foundation for integrated photonics beyond nanowire waveguides of silicon and silicon nitride. This technology is promising for more compact and deeper photonic integration such as right angle bends, more compact modulators, slow light and interfacing with single photon emitters for photonic integrated circuits, quantum communications, and biosensing. [ABSTRACT FROM AUTHOR]

Long regarded as a model system for studying insulator-to-metal phase transitions, the correlated electron material vanadium dioxide (VO2) is now finding novel uses in device applications. Two of its most appealing aspects are its accessible transition temperature (~341 K) and its rich phase diagram. Strain can be used to selectively stabilize different VO2 insulating phases by tuning the competition between electron and lattice degrees of freedom. It can even break the mesoscopic spatial symmetry of the transition, leading to a quasiperiodic ordering of insulating and metallic nanodomains. Nanostructuring of strained VO2 could potentially yield unique components for future devices. However, the most spectacular property of VO2--its ultrafast transition--has not yet been studied on the length scale of its phase heterogeneity. Here, we use ultrafast near-field microscopy in the mid-infrared to study individual, strained VO2 nanobeams on the 10 nm scale. We reveal a previously unseen correlation between the local steady-state switching susceptibility and the local ultrafast response to below-threshold photoexcitation. These results suggest that it may be possible to tailor the local photoresponse of VO2 using strain and thereby realize new types of ultrafast nano-optical devices. [ABSTRACT FROM AUTHOR]

3D surface topography is simulated using Boundary Element Method (BEM) by computing far field scattered by a metallic or dielectric nanosphere which scans in the near field region of an arbitrary rough surface. Nanosphere is considered as NSOM probe's tip and two scanning modes, Constant Height Mode (CHM) and Constant Distance Mode (CDM) are simulated. Our results show that resolution and image quality are enhanced by decreasing scanning sphere's height or diameter in CHM. Also, image quality in Transverse Magnetic (TM) polarization is higher compared with Transverse Electric (TE) polarization. In TM polarization for both scanning mode CHM and CDM, Aluminum scanner makes a better image quality in comparison to dielectric sphere. However in TE polarization, electric field intensity scattered by a dielectric sphere is higher compared with Aluminum sphere. In spite of higher image quality in CHM, image quality is not satisfactory in CDM and image does not show a perfect match with the surface topography. High precision, speed, and low amount of data during the calculations are advantages of BEM in comparison to other numerical methods. [ABSTRACT FROM AUTHOR]

The migration of mesenchymal stem cells (MSCs) plays a key role in tumor-targeted delivery vehicles and tumor-related stroma formation. However, there so far has been no report on the distribution of cell surface molecules during the VEGF-induced migration of MSCs. Here, we have utilized near-field scanning optical microscopy (NSOM) combined with fluorescent quantum dot (QD)-based nano-technology to capture the functional relationship between CD44 and CD29 adhesion molecules on MSCs and the effect of their spatial rearrangements. Before VEGF-induced migration of MSCs, both CD44 and CD29 formed 200–220 nm nano-domains respectively, with little co-localization between the two types of domains. Surprisingly, the size of the CD44 nano-domain rapidly increased in size to 295 nm and apparently larger aggregates were formed following MSC treatment with VEGF for 10 min, while the area of co-localization increased to 0.327 μm 2 . Compared with CD44, CD29 was activated obviously later, for the fact that CD29 aggregation didn't appear until 30 min after VEGF treatment. Consistently, its co-localization area increased to 0.917 μm 2 . The CD44 and CD29 nano-domains further aggregated into larger nano-domains or even formed micro-domains on the membrane of activated MSCs. The aggregation and co-localization of these molecules promoted FAK formation and cytoskeleton rearrangement. All of the above changes induced by VEGF contributed to MSC migration. Taken together, our data of NSOM-based dual color fluorescent imaging demonstrated for the first time that CD44, together with CD29, involved in VEGF-induced migration of MSCs through the interaction between CD44 and its co-receptor of VEGFR-2. [ABSTRACT FROM AUTHOR]

Plasmonic metasurfaces are investigated that consist of a sub‐wavelength line pattern in an ultrathin (∼10 nm) silver film, designed for extraordinary suppressed transmission (EOST) in the visible spectral range. Measurements with a near‐field scanning optical microscope (NSOM) demonstrate that far‐field irradiation resonantly excites antenna‐like (bright) modes that are localized on the metal ridges. The re‐radiation of these modes into the far‐field interferes destructively with the transmitted wave, thus suppressing transmission almost completely. In contrast, a second type of mode, bound (dark) surface plasmon polaritons (SPPs) launched from an NSOM tip, propagates well across the metasurface, preferentially perpendicular to the grating lines. [ABSTRACT FROM AUTHOR]

Amendments have been made to International Standard ISO 18115-2:2010, extending the number of terms and, in a few cases where usage has changed, incorporating revisions. Part 2 covers 277 terms used in scanning probe microscopy as well as 98 acronyms. The terms cover words or phrases used in describing the samples, instruments and theoretical concepts involved. © 2014 Crown copyright. Surface and Interface Analysis © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Surface arrays of photoactive materials with subwavelength dimensions are important for energy harvesting applications due to their capacity for broadband and omnidirectional absorption of the solar radiation. It was recently proposed and demonstrated that the absorption performance of such arrays can be further amplified with the introduction of additional nano-features. In the current work we consider the incorporation of nano-features into nanopillar (NP) arrays. The considered nano-features are: quasi-nanolenses, sidewall nano-decorations, and decreasing the NP bottom diameter to transform it into a light funnel (LF). The underlying various light trapping mechanisms are examined using near-field microscopy. Near-field microscopy is used to obtained both high-resolution far-field imaging, as well as mapping of the near-field photon distributions of the arrays. Firstly, it is shown that the main contribution to far-field reflected photons is from the ambient surrounding the silicon structures. Secondly, the incorporation of the various nano-features induces a decrease in the reflected far-field photons which originate from this ambient region. Also, it is shown how the incorporation of quasi-nanolenses concludes a decrease in far-field photons reflected in the oblique directions with high polar angles, whereas the incorporation of sidewall nano-decorations leads to a decrease in far-field photons reflected in directions of small polar angles. Also, the incorporation of both qNL and sidewall nano-decorations is examined, and light trapping with the LF geometry is discussed and demonstrated. Finally, understanding the underlying light trapping mechanisms will support the deterministic design of subwavelength arrays incorporated with nano-features for efficient harvesting of the solar radiation. [Display omitted] • Nano-features for broadband absorption of the solar radiation. • High-resolution far-field imaging of subwavelength arrays incorporated with nano-features. • Near-field photon imaging for the determination of solar absorption. • Determination of light trapping mechanisms with near-field optical microscopy. [ABSTRACT FROM AUTHOR]

Near-field scanning optical microscope (NSOM) measurements revealed that a linearly polarized Gaussian beam of wavelengthλ = 532 nm focused with a binary zone plate (ZP) of focal lengthλ, radius 7 μm, and groove depth 510 nm, fabricated in hydrogen silsesquioxane, produces a focal spot of size FWHM = (0.44 ± 0.02)λ, with the side lobes being lower than 10% of the intensity peak in the focus. Replacing the incident 532 nm wavelength with a 633 nm wavelength resulted in a 1.8 times shorter focal length and a tighter (in terms of wavelengths) focal spot of FWHM = (0.40 ± 0.02)λ. This value is smaller than the scalar diffraction-limited size in vacuum, FWHM = 0.51λ. This is the smallest focal spot so far experimentally obtained for a binary phase ZP and the root-mean-square deviation of the experimental curve from a FDTD simulation is 5%. We show that the metallic pyramid-shaped cantilever with a 100-nm-hole in the tip that is used in the NSOM is only able to detect the transverse electric field component. The FDTD simulation showed such a cantilever to be over 3 times more sensitive to the transverse electric field component than to the longitudinal one. Using the Richards–Wolf (RW) formulae, the near-focus intensity distribution can be calculated with 6% error for focal lengths larger than 4λ. It is usually assumed that the Debye theory and the RW formulae are only valid for focal lengths much larger than the incident wavelength. By FDTD simulation, we showed that when illuminating the ZP by a radially (rather than linearly) polarized beam, a decrease in the focal spot transverse size did not result in a substantially reduced total volume of focus (4%). [ABSTRACT FROM PUBLISHER]

Over the last decade or so a group of us, while working at Bell Labs, have been able to develop a large number of silicon micromachines for a wide range of applications. In this article, which is part of a special volume to celebrate the career of Professor Francis Gasparini who is an old friend and colleague, we review the devices we have been able to build and discuss their applications. These applications range from scientific experiments looking at single vortex dynamics and the observation of the Casimir effect to technological applications such as a large, all-optical switch. In this article we make the point that MEMS devices and VLSI processing are the 'New Physics Machine Shop'. [ABSTRACT FROM AUTHOR]

We demonstrated the near-field optical transmission properties of nanogratings with spoke and rings structures through a near-field scanning optical microscope, and the far-field optical transmission properties with different polarization angles are investigated with an optical microscope. Our experimental results verified the polarization properties of the nanograting structures and further demonstrated the experimental results are supported by the finite difference time domain theoretical simulation. The optical microscope imaging of the spoke and ring structures also show that the grating structures can disperse visible light of different wavelengths. [ABSTRACT FROM AUTHOR]

Cellular uptake behavior of iron oxide nanoparticles is investigated using a transmission near-field scanning optical microscopy (NSOM) without the need of fluorescent labeling. By using the transmission NSOM system, we could simultaneously explore the near-field optical analysis of the cell interior and record the topographic information of the cell surface. The cell endocytosis of iron oxide nanoparticles by normal breast MCF10A cells is first studied by this transmission NSOM system, and this dual functional nanoscale-resolution microscopy shows the capability of mapping the spatial localization of nanoparticles in/outside cell surface without the need of fluorescence labeling. Nanoscale optical signature patterns for iron oxide nanoparticle-loaded vesicles inside the cells were observed and analyzed. [ABSTRACT FROM AUTHOR]

Band gap fluctuations and carrier localization in AlxGa1-xN films with x values varying from 0.30 to 0.50 has been studied by scanning near-field optical microscopy (SNOM) by measuring photoluminescence. The measurements have revealed a dual localization potential. Microscopic scale potential variations, detected by the SNOM, were most pronounced in the lower Al content samples. The nanoscopic carrier localization potentials, evaluated from the width of the photoluminescence spectra, were largest in layers with the largest AlN molar fraction. The large scale potential fluctuations were attributed to Ga rich regions close to grain boundaries or atomic layer steps. The density, size and band gap energy of these domains were found to be composition dependent. The nanoscopic potential variations have been assigned to small-scale compositional fluctuations, possibly, occurring due to formation of Al rich grains during growth. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The surface plasmons properties on gold film composed of inverted square pyramidal pits were investigated. The near-field scanning optical microscopy image showed that the surface plasmons were mainly located in the cavity of the pits; this is consistent with the mapping image obtained using the Raman scattering intensity of Rhodamine 6G. The calculation results obtained by using the finite element method showed that the electric field mainly located in the pyramidal pits and the field distribution was not affected by the adjacent pits around it. Compared with the single pyramidal pit, the localized electric field intensity increased in the condition of the structure array because of the surface plasmons coupling effect. The surface-enhanced Raman scattering spectra intensity decreased as the incident angle of the excited laser increased except that there are two peaks at around 5° and 17.5°, which can be attributed to the Bragg scattering of the surface plasmons. The reflectance spectra collected by a microscope at different magnifications were different. The intensity variation between surface-enhanced Raman scattering spectra obtained using ×20 and ×50 objective illustrated that the adsorption peak in the reflectance spectra corresponded to the surface plasmons coupling effect. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Nano-spatial distribution of cell surface molecules on cell membrane fluctuations during T-cell activation has not been reported. In this study, we innovated application of near-field scanning optical microscopy (NSOM)/quantum dots (QDs)-based nanotechnology through three-dimensional image fusion algorithm to merge the simultaneously obtained dual-color fluorescence information and three-dimensional topography. This novel imaging system made it possible to visualize nano-spatial distribution and organization of early-activation molecules CD69 and late-activation molecules CD71 on cell-membrane fluctuations during T-cell activation. Interestingly, most CD69 molecules were clustered to form 250–500nm nano-domains polarizing predominantly in the peak of the cell-membrane fluctuations. In contrast, although CD71 molecules were also clustered as 250–500nm nano-domains, they polarized dominantly in the valley of the cell-membrane fluctuations. The peak–valley polarities of CD69 nano-domains and CD71 nano-domains implied their different functions. CD69 nano-domains polarizing on membrane-peak fluctuations might serve as transient platforms driving TCR/CD3-induced signaling and activation, whereas CD71 nano-domains distributing in the membrane-valley fluctuations appeared to facilitate iron uptake for increased metabolisms in T-cell activation. Importantly, this NSOM/QD-based fluorescence–topographic image fusion provides a powerful tool to visualize nano-spatial distribution of cell-surface molecules on cell-membrane fluctuations and enable better understanding of distribution–function relationship. [Copyright &y& Elsevier]

Three types of indirect phase tuning-based plasmonic structures with subwavelength circular grooves/slits and/or central apertures corrugated on Au film supported by glass substrate: depth modulation, width modulation, and hybrid depth-width modulation, were put forth in this paper. They were investigated experimentally by means of nanofabrication and near-filed scanning optical microscope characterization. The plasmonic structures were fabricated using the technique of focused ion beam direct milling. Our experimental results demonstrated that all of the phase tuning-based structures have focusing functions. Both the width and depth modulation-based structures can realize beam focusing and produce an elongated depth of focus. Moreover, after comparison among these three structures, we found that the width modulation-based structure has the best focusing performance. [ABSTRACT FROM AUTHOR]

n elliptical nano-pinhole structure-based plasmonic lens was designed and investigated experimentally by means of focused ion beam nanofabrication, atomic force microscope imaging, and scanning near-field optical microscope (NSOM). Two scan modes, tip scan and sample scan, were employed, respectively, in our NSOM measurements. Both the scan modes have their characteristics while probing the plasmonic lenses. Our experimental results demonstrated that the lens can realize subwavelength focusing with elongated depth of focus. This type of lens can be used in micro-systems such as micro-opto-electrical-mechanical systems for biosensing, subwavelength imaging, and data storage. [ABSTRACT FROM AUTHOR]

Gold nanohole arrays are fabricated with focused ion beam irradiating gold thin film supported on quartz substrate. The topography of the nanohole arrays is characterized using an atomic force microscope, and the near-field optical transmission properties of the nanohole array are investigated with a near-field scanning optical microscope. Our experimental results verify the near-optical transmission performance and further demonstrate that they are in agreement with the theoretical calculation results. The enhanced optical transmission of the nanohole arrays are expected to be used for a variety of applications in sensor and photonics devices. [ABSTRACT FROM AUTHOR]

In thin-film silicon solar cell devices randomly textured interfaces are used to achieve light scattering sufficient for efficient light trapping. We use near-field scanning optical microscopy (NSOM) for visualizing wave guiding mechanisms experimentally by measuring the evanescent modes. Their impact on the light trapping efficiency and the link to topographic structures will be addressed. [ABSTRACT FROM AUTHOR]

Multipolar plasmon optical excitations at spherical gold nanoparticles and their manifestations in the particle images formatted in the particle surface proximity are studied. The multipolar plasmon size characteristic: plasmon resonance frequencies and plasmon damping rates were obtained within rigorous size dependent modelling. The realistic, frequency dependent dielectric function of a metal was used. The distribution of light intensity and of electric field radial component at the flat square scanning plane scattered by a gold sphere of radius 95 nm was acquired. The images resulted from the spatial distribution of the full mean Poynting vector including near-field radial components of the scattered electromagnetic field. Monochromatic images at frequencies close to and equal to the plasmon dipole and quadrupole resonance frequencies are discussed. The changes in images and radial components of the scattered electromagnetic field distribution at the scanning plane moved away from the particle surface from near-field to far-field region are discussed. [ABSTRACT FROM AUTHOR]

This article presents results of near-field scanning optical microscope measurement of local luminescence of rhodamine 3B intercalated in montmorillonite samples. We focus on how local topography affects both the excitation and luminescence signals and resulting optical artifacts. The Finite Difference in Time Domain method (FDTD) is used to model the electromagnetic field distribution of the full tip-sample geometry including far-field radiation. Even complex problems like localized luminescence can be simulated computationally using FDTD and these simulations can be used to separate the luminescence signal from topographic artifacts. [ABSTRACT FROM AUTHOR]

Abstract: The evanescent field surrounding the core of an optical waveguide is very sensitive to refractive index changes near the core. This sensitivity can be exploited to form the basis for a quantitative sensor with high specificity and sensitivity. Selective probe molecules may be attached to the surface of a waveguide core and the evanescent field locally monitored as target analytes are introduced to the system. In this study, probe/analyte regions were simulated using lithographically patterned organic films with thicknesses of 60nm and 130nm. The evanescent field strength was measured quantitatively using near field scanning optical microscopy (NSOM). The presence of the organic material on the waveguide caused up to a 70% change in the intensity of the evanescent field over the patterned region and the excitation of a weakly bound higher order mode. The waveguide core and surrounding cladding were numerically simulated using the beam propagation method and these predictions are in quantitative agreement with the experimental results obtained using NSOM. [Copyright &y& Elsevier]

Abstract: A novel system has been developed for the imaging of carrier transport within semiconductor nanostructures by operating a near field scanning optical microscopy (NSOM) within a scanning electron microscope. Luminescence associated with carrier recombination is collected with high spatial resolution to monitor the motion and recombination of charge generated by use of an electron beam as an independent point source. Light is collected in the near field from a scanning fiber using tuning fork feedback in an open architecture combined AFM/NSOM system allowing independent motion of sample and tip. From a single image, it is possible to obtain a direct measure of minority carrier diffusion length. This technique has been used in the near-field collection mode to image the diffusion of holes in n-type GaN–AlGaN core-shell nanowires, grown via Ni-catalyzed MOCVD. Measurements were made on tapered nanowires ranging in diameter from 500 to 800nm, with lengths up to ∼30μm. The average 1-dimensional carrier diffusion length was measured to be 1.2±0.2μm in the low injection limit. In addition, it is possible to map the luminescence that is waveguided to the end of the structure, imaging waveguide modes. [Copyright &y& Elsevier]

Characterization issues of plasmonic structures are highlighted and investigated in detail in this paper. Combining with the plasmonic structures functioning for sub-wavelength focusing, optical characterization was carried out using a near-field scanning optical microscope (NSOM) system. Characterization errors that originated from both the nanofabrication using a focused ion beam (FIB) direct milling technique and misalignment of the NSOM system were analyzed in comparison to the theoretical computational results. Our experimental results demonstrated that the focusing function of the structures is in agreement with that of the designed structure. However, the measured beam spot size is larger than the designed value due to the direct measurement error originating from the NSOM and the indirect error from the FIB fabrication process. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the improvement of polymer microlenses at the extremity of an optical fiber. The process reported previously involves a spatially controlled light-induced polymerization within a drop of liquid photopolymerizable formulation deposited on the end of a cleaved fiber. The process is of highest interest for applications in optical connecting and optical fiber sensor since it is fast, highly flexible (curvature radii ranges from 0.2 to 200μm) and does not require expensive equipment. In particular, the spatial extend of the photopolymerization was demonstrated to be highly dependent on physico-chemical parameters of the formulation. The influence of parameters that govern the photopolymerization reaction and light propagation in the photopolymerizable medium such as irradiation time, light power, oxygen quenching and dye absorption, were studied in order to control the final properties of the polymer tip. The present study allowed selecting the synthesis parameters leading to well-controlled geometrical structures. From a fundamental point of view, this study appeared to be an interesting means to investigate the photostructuration of polymers at the micro- and nanoscales. [Copyright &y& Elsevier]

Abstract: We have developed a simple and accurate method for calibrating the amplitude of vibration of quartz tuning fork sensors commonly used in atomic force- and near field optical-microscopy. Unlike interferometric methods, which require a complex optical setup, the method we present requires only a simple measurement of the electro-mechanical properties of the tuning-fork oscillator and can be performed in a matter of minutes without disturbing the experimental setup. Comparison with interferometric methods shows that an accuracy of better than few percent can be routinely achieved. [Copyright &y& Elsevier]

Abstract: Using a near-field scanning optical microscope, near-field photocurrent and topographic imaging has measured the effect on intrinsic electric fields and photocurrent propagation resulting from inserting multi-quantum barrier (MQB) super-lattices into quantum well lasers. Measurements on devices at two different excitation wavelengths have highlighted the sensitivity of the near-field optical technique. Strong correlations were seen in the photocurrent response of the multi-quantum barrier regions when compared with simulations made on the electric field generated within the structure. As a result, photocurrent attenuation was attributed to carrier confinement in these barrier regions when compared to a control sample. The measurements illustrate the effectiveness of the MQB, in addition to the sensitivity and power of the near-field photocurrent technique. [Copyright &y& Elsevier]

Abstract: In this article results of a comparison of two NSOM probe characterization methods are presented. Scanning electron microscopy analysis combined with electromagnetic field modeling using the finite difference in time domain method are compared with measured far-field radiation diagrams of NSOM probes. It is shown that measurement of far-field radiation diagrams can be an efficient tool for daily checking of the NSOM probes quality. Moreover, it is shown that the inner probe geometry has large influence on the directional radiation of an NSOM probe and the far-field radiation diagram can be used as a simple method to distinguish between different probe geometries. [Copyright &y& Elsevier]

Abstract: In this article, the results of the modeling of topography related artifacts appearing in near-field scanning optical microscopy measurements are presented. The results obtained for near-field scanning optical microscope operation in reflection mode with off-axis far field detector position are compared with experimental results. It is shown that the chosen numerical method – Finite Difference in Time Domain method (FDTD) – can be used for efficient modeling of main topography related artifact. It is also seen that the far field detector position can have large influence on the resulting reflection mode optical images. [Copyright &y& Elsevier]

Amplitude and phase measurements of the near-field generated by isolated subwavelength apertures in a gold film are presented. The near-field distribution of such a structure is complex and the measured signal strongly depends on the electric field components effectively detected by the experimental setup. By comparing this signal with 3D vectorial calculations we are able to determine which electric field components are effectively measured. The sensitivity of the phase distribution is key to this measurement. The proposed characterization technique should prove extremely useful to calibrate a Scanning near-field optical microscopy (SNOM) beforehand in order to retrieve quantitative information on the polarization of the field distribution under study. [ABSTRACT FROM AUTHOR]

Near-field optical probe is the key element of a near-field scanning optical microscopy (NSOM) system. The key innovation in the first two NSOM experiments ( Pohl et al., 1984 ; Lewis et al., 1984 ) is the fabrications of a sub-wavelength optical aperture at the apex of a sharply pointed transparent probe tip with a thin metal coating. This paper discusses the routine use of focussed ion beam (FIB) to micro-machine NSOM aperture probes from the commercial silicon nitride cantilevered atomic force microscopy probes. Two FIB micro-machining approaches are used to form a nanoaperture of controllable size and shape at the apex of the tip. The FIB side slicing produces a silicon nitride aperture on the flat-end tips with controllable sizes varying from 120 nm to 30 nm. The FIB head-on drilling creates holes on the aluminium-coated tips with sizes down to 50 nm. Nanoapertures in C and bow tie shapes can also be patterned using the FIB head-on milling method to possibly enhance the optical transmission. A transmission-collection NSOM system is constructed from a commercial atomic force microscopy to characterize the optical resolution of FIB-micro-machined aperture tips. The optical resolution of 78 nm is demonstrated by an aperture probe fabricated by FIB head-on drilling. Simultaneous topography imaging can also be realized using the same probe. By mapping the optical near-field from a bow-tie aperture, optical resolution as small as 59 nm is achieved by an aperture probe fabricated by the FIB side slicing method. Overall, high resolution and reliable optical imaging of routinely FIB-micro-machined aperture probes are demonstrated. [ABSTRACT FROM AUTHOR]

Plasmon resonances in 3D nanoparticle arrangements can produce strong localized optical fields, which are of importance for any application involving interaction of light with subwavelength volumes of matter down to the molecular level. In particular, remarkable field enhancement and confinement occur in a dimer geometry formed by two identical closely spaced particles. Although, recent advances in nanofabrication have rendered the fabrication of complex plasmon architectures more accessible, addressing their local fields in a nonperturbative fashion remains not straightforward, because metallic nanostructures are rather sensitive to their local environment. Here we study gold dimers fabricated by e-beam lithography. Individual dimers are imaged both by far- and near-field methods. First, the near-field electromagnetic interaction in an ensemble of dimers is investigated by scattering spectroscopy, using dark field microscopy. Next, to probe their local field, we explore the luminescence of individual gold dimers utilizing a confocal microscope with single molecule detection sensitivity. We provide a statistical analysis of the dimer luminescence for different incident polarizations, with direct comparison to single particles (monomers). Finally, the near-field transmission of the resonant dimers is mapped with a subwavelength resolution using polarized controlled near-field scanning optical microscopy. Surprisingly, no clear evidence of the high mode density in the dimer gap is observed. This result may be attributed to the limited coupling of the field emitted by the aperture probe to the dimer mode. [ABSTRACT FROM AUTHOR]

To elucidate the optical coupling nature of near-field scanning optical microscope (NSOM) probes we observed by a NSOM the lasing field of commercial laser diodes (LDs) on their cleaved surface that was expected to be an ideal single TE00 mode and be polarized perpendicular to the probe axis. A clear dark region was observed at the lasing active region of the LD, indicating that the optical probe coupled only the target near-field polarized parallel to the probe's long axis. Many concentric bright rings, detected in the near-field emission profile extending outside of the optical guide layer, should be polarized perpendicular to the TE00 mode, and were ascribed to amplified spontaneous emissions from recombination between an electron and a light hole, based on the symmetry of radiation field. Another possibility was an optical coupling between the optical probe and the laser diode cavity, which might modify the original field distribution inside the laser diode cavity. In both cases the observation suggests that a near-field probe works as a novel tool to manipulate the cavity electromagnetic field, which is a common issue to many applications of cavities made from organic ultrathin films. [ABSTRACT FROM AUTHOR]