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An overview of near-field optics is presented with a focus on the fundamental advances that have been made in the field since its inception 30 years ago. A focus is placed on the advancements that have been achieved in instrumentation. These advances have led to a greater generality of use with ultra-low mechanical and optical noise and the ultimate in force sensitivity with near-field optical probes. An emphasis is placed on the importance of fully integrating near-field optics with other imaging and spectroscopic modalities including Raman spectroscopy and electron/ion beam imaging. Important directions in probe design, force feedback methods and scanner flexibility are described. These developing avenues provide considerable optimism for an ever increasing incorporation of near-field optics to help resolve critical problems in fundamental and applied science.

In surface science, water adsorption on hydrophilic samples is usually invoked, addressing their nanoscale experimental effects in scanning probe microscopy, especially when water condensates between tip and sample. Here we study by means of a numerical hybrid method the effect of water bridge formation in near field imaging. We show how this nanometric water neck plays an important role not only in the optical image, producing a high contrast at hydrophilic patches, but also in the tip-sample distance control. This work contributes with a new methodology able to retrieve the original application of SNOM, using it as an instrument to study the optical properties of matter overcoming the diffraction limit. It extends the application of SNOM to study the hydrophilic character of polymeric and biological samples, taking advantage of ubiquitous effect of humidity when operating in ambient condition. © 2013 Elsevier B.V., This work has been funded through projects FIS2009-13403-C02-01(MICINN), S2009/MAT-1467(CAM) and CSD2010-00024(MICINN).

Surface plasmon-polaritons are a possible solution for on-chip transportation and manipulation of information. Although there are several possibilities for designing the plasmonic waveguides, the two major caveats for all of them are the coupling to/from external sources and the losses they exhibit. In this work we will present an overview of our simulation, fabrication and characterisation activity in the plasmonic field where we tackle these issues. We start with presenting an optimised nanoantenna for coupling of free-propagating waves into a subwavelength slot waveguide modes. Optimised antennae show an increase in coupling efficiency up to 185 times compared to a bare waveguide. Once optimized, the nanoantennae were fabricated and the propagation in the slot waveguides was characterised. The characterisation shows an increase in the effective area (proportional to the coupling efficiency) of up to 175 times, similar to the calculated optimised parameters. We then move our attention to effective tapering of the plasmonic modes such that to achieve either strong field enhancement or propagation into thin plasmonic nanowires. Using on-chip nanofocusing with impedance-matched nanoantenna we can obtain a field enhancement of up to ∼ 12000 evenly distributed in a volume of ∼ 30x 30 x 10 nm3. The same taper can be used also for modifying the waveguide profile from a wide strip waveguide to a nanorod waveguide showing both the flexibility of our taper design as well as allowing to measure and compare the propagation characteristics in waveguides with various widths. We show that the propagation length matches very well the theoretical one and also obtain a limit for confinement of the mode in this type of plasmonic waveguides of ∼ λ/15.

We present a fully implemented Infrared (IR) Scanning Near-field Optical Microscopy (SNOM) in spectroscopic mode for tissue imaging and early cancer diagnostics.

This work reports the use of an infrared spectroscopic version of scanning near-field optical microscopy (IR-SNOM) and shows that it is possible to reveal subcellular entities via their chemical constituents in a label-free human oesophageal adenocarcinoma cell (OE33). This work presents the first high spatial resolution (similar to 0.15 mu m) study of features imaged at various wavelengths within a cancer cell. The clear illumination of sub-micron sized moieties within a cell is a major step forward and is a key requirement for understanding cancer and for the study of other diseases and healthy tissue. The stable and tuneable light source was provided by the infrared free electron laser on the ALICE accelerator at Daresbury. The images reveal a structure with a size and wavelength absorption that are consistent with a chromosome and open the possibility of observing other localized structures, such as microvesicles, that play an important role in the development and spread of cancers.

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.

Human HaCaT cells, exposed for 24 h to a 1 mT (rms) 50 Hz sinusoidal magnetic field in a temperature-regulated solenoid, suffer detectable changes in their biochemical properties and shapes. By using infrared wavelength-selective scanning near-field optical microscopy, we observed changes in the distribution of the inner chemical functional groups and in the cell morphology with a resolution of 80-100 nm.

9 - Conference paper: 9th International Conference on Near-Field Optics, Nanophotonics and Related Techniques, SEP 10-15 2006, Lausanne (SWITZERLAND); In this paper, we study the performances of nanosensors based on Localized Surface Plasmon Resonance in the context of biological sensing. We demonstrate the sensitivity and the selectivity of our designed nanosensors by studying the influence of the concentration of Streptavidin on the shift of Localized Surface Plasmon Resonance wavelength. In addition, to study the detection of biomolecules on a single Au nanoparticle, we used a Scanning Near-field Optical Microscope. These results represent new steps for applications in biological research and medical diagnostics.

Topographic and optical contrasts formed by Ga+ ion irradiation of thin films of amorphous silicon carbide have been investigated with scanning near-field optical microscopy. The influence of ion-irradiation dose has been studied in a pattern of sub-micrometre stripes. While the film thickness decreases monotonically with ion dose, the optical contrast rapidly increases to a maximum value and then decreases gradually. The results are discussed in terms of the competition between the effects of ion implantation and surface milling by the ion beam. The observed effects are important for uses of amorphous silicon carbide thin films as permanent archives in optical data storage applications.

We first investigate the microscopic working principle of the nanowire superconducting single-photon detectors (SSPDs), and we find that the edge of the nanowire is much more sensitive than the central part. The experimental results agree quantitatively with the theory based on a photon-assisted vertex- entry model. We then explore its potential to be used as a probe for near-field detection. Our calculations show that the SSPDs have a much higher signal collection efficiency than the conventional near-field optical microscopy, and that their spacial resolution can reach 20 nm. With photon number resolving ability, a SSPD fabricated on a micro-pillar can be used to investigate the quantum information of the optical near-field at subwavelength scales.

Metal nanoshells composed by a dielectric core with a thin gold layer are stimulating growing interests due to the unique optical, electric and magnetic properties exhibited by the local field enhancement near the metal - dielectric core interface due to strong local plasmon resonance and the high tunability of such resonance as a function of shape and core-material. These unique characteristics have found promising applications in a wide range of areas, such as biosensing, optical communication and medicine. In this paper, we developed a theoretical and numerical simulation based on a near-field approach to study the possibility to identify nanoshells inside mouse cells. Taking advantage from the characteristic near-infrared transparency window of many biological systems, i.e. the low light absorption coefficient of biological systems between 750-1100nm, we show the possibility to identify and detect 100-150nm diameter gold nanoshells inside the animal cells.

Bitumen and bituminous binders are a mixture of a wide variety of molecules with different size and nature; a-polar as well as polar, aromatic as well as aliphatic, chain-like as well as two-dimensional in nature. However, most of the bitumina display at ambient temperatures a spontaneous formation of micro-phases displaying different mechanical properties such as stiffness or adhesive behaviour. The actual chemical composition of the individual phases is still a matter/subject of discussion. The application of different scanning probe microscopy modes such as FFM, SThM and SNOM enabled the investigation of the relationships between asphalt microstructure and material characteristics such as friction coefficient, thermal conductivity and chemical composition and polarity. It was possible to collect data providing more and detailed information's on a nano-scale and in detail with respect to the different micro-phases present in bituminous binders. All data collected fit into the present picture of structuring of bitumen and the characteristics of the present phases.

The following dissertation examines the tunability of two types of proof-of-concept devices centering around post-fabrication modification of the infrared optical response. The first device, created through the hybridization of the metamaterials and the phase-transition oxide vanadium dioxide (VO2), is probed using Fourier transform infrared spectroscopy. We demonstrate that, through application of voltage pulses to this initially uniform device, a gradient in the optical properties can be obtained. This macroscopic control mechanism enables persistent modification of the device, though the hysteretic nature of the VO2 insulator to metal transition (IMT), on spatial scales on the order of a few wavelengths of the probing light. In addition to effects from current-induced heating, we show that the optical response can also be modified through the use of an ionic gel to oxidize or reduce the vanadium ions in VO2, thereby driving its IMT. These measurements also demonstrate the potential for metamaterials as a means of probing metal-to-insulator transitions, allowing for enhanced optical probing of changes in VO2 properties due to electric fields from the ion gel. The second device we explored is a graphene based device used for examining the modification of graphene’s plasmonic response in conjunction with the ferroelectric high-κ dielectric lead zirconium titanate (PZT) employed as a gate dielectric. By using PZT, the carrier concentration, and therefore the optical properties of graphene, can be heavily modified with small back-gate voltages. Additionally, the use of a ferroelectric dielectric enables a form of memory in the device where transient voltage application leads to persistent changes in graphene properties. Examination of this device using scanning near-field optical microscopy allows us to determine the usefulness of similar devices in future plasmonic device.

Graphene plasmons were predicted to possess simultaneous ultrastrong field confinement and very low damping, enabling new classes of devices for deep-subwavelength metamaterials, single-photon nonlinearities, extraordinarily strong light–matter interactions and nano-optoelectronic switches. Although all of these great prospects require low damping, thus far strong plasmon damping has been observed, with both impurity scattering and many-body effects in graphene proposed as possible explanations. With the advent of van der Waals heterostructures, new methods have been developed to integrate graphene with other atomically flat materials. In this Article we exploit near-field microscopy to image propagating plasmons in high-quality graphene encapsulated between two films of hexagonal ​boron nitride (h-BN). We determine the dispersion and plasmon damping in real space. We find unprecedentedly low plasmon damping combined with strong field confinement and confirm the high uniformity of this plasmonic medium. The main damping channels are attributed to intrinsic thermal phonons in the graphene and dielectric losses in the h-BN. The observation and in-depth understanding of low plasmon damping is the key to the development of graphene nanophotonic and nano-optoelectronic devices.

Bitumen and bituminous binders are a mixture of a wide variety of molecules with different size and nature; a-polar as well as polar, aromatic as well as aliphatic, chain-like as well as two-dimensional in nature. However, most of the bitumina display at ambient temperatures a spontaneous formation of micro-phases displaying different mechanical properties such as stiffness or adhesive behaviour. The actual chemical composition of the individual phases is still a matter/subject of discussion. The application of different scanning probe microscopy modes such as FFM, SThM and SNOM enabled the investigation of the relationships between asphalt microstructure and material characteristics such as friction coefficient, thermal conductivity and chemical composition and polarity. It was possible to collect data providing more and detailed information's on a nano-scale and in detail with respect to the different micro-phases present in bituminous binders. All data collected fit into the present picture of structuring of bitumen and the characteristics of the present phases.

We derived a simple method to fabricate STM-SNOM hybrid probes obtained from commercial cheap communication optical fibers. The tips are fabricated by a methodology that combines two well-known techniques: the selective attack by a buffered solution and the protected layer chemical etching, in a single new one-step technique. The tailored probes are then sputtered by metal and mounted on a STM setup. The usual difficulties of integrating the optical fiber in the STM head are solved originally with a particular home made mount described in details. We will show that the resulting probes reach atomic resolution on both vertical and horizontal scale, and that the optical imaging is free of artifacts and satisfactory with a lateral resolution in the order of λ/20, as far as we know the finest resolution obtained with a system based on a hybrid fiber probe. We believe that our methodology is very interesting for its simplicity of realization and for the good resolving power in both SNOM and STM modes.

We report about the polarization properties of light transmitted by hollow pyramidal SNOM tips. The use of a thin polymeric dichroic film allowed us to clearly distinguish between the behavior in the near-field and in the far-field regime and to emphasize strong differences between them: while in the far-field region a pinning of the polarization can take place, in the near-field region the in-plane polarization always follows linearly that of the light incident on the tip, for all the measured tips. These original findings stress the very peculiar nature of the evanescent field in the near-field regime, and have important consequences for all the applications of polarized light in near-field microscopy. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

High-resolution analysis of activities of live cells is limited by the use of non-invasive methods. Apparatuses such as SEM, STM or AFM are not practicable because the necessary treatment or the harsh contact with system probe will disturb or destroy the cell. Optical methods are purely non-invasive, but they are usually diffraction limited and then their resolution is limited to approximately 1 μm. To overcome these restrictions, we introduce here the study of membrane activity of a live cell sample using a Scanning Near-field Optical Microscope (SNOM). A near field optical microscope is able to detect tiny vertical movement on the cell membrane in the range of only 1 nm or less, about 3 orders of magnitude better than conventional optical microscopes. It is a purely non-invasive, non-contact method, so the natural life activity of the sample is unperturbed. In this report, we demonstrated the nanometer-level resolving ability of our SNOM system analyzing cardiomyocytes samples of which membrane movement is known, and then we present new intriguing data of sharp 40 nm cell membrane sudden events on rat pheochromocytoma cell line PC12. All the measurements are carried out in culture medium with alive and unperturbed samples. We believe that this methodology will open a new approach to investigate live samples. The extreme sensitivity of SNOM allows measurements that are not possible with any other method on live biomaterial paving the way for a broad range of novel studies and applications.

Scanning near-field optical microscopy (SNOM or NSOM) is the technique with the highest lateral optical resolution available today, while infrared (IR) spectroscopy has a high chemical specificity. Combining SNOM with a tunable IR source produces a unique tool, IR-SNOM, capable of imaging distributions of chemical species with a 100 nm spatial resolution. We present in this paper boron nitride (BN) thin film images, where IR-SNOM shows the distribution of hexagonal and cubic phases within the sample. Exciting potential applications in biophysics and medical sciences are illustrated with SNOM images of the distribution of different chemical species within cells. We present in this article images with resolutions of the order of λ/60 with SNOM working with infrared light. With our SNOM setup, we routinely get optical resolutions between 50 and 150 nm, regardless of the wavelength of the light used to illuminate the sample.

The advent of scanning near-field optical microscopy (SNOM) has augmented at a microscopic level the usefulness of optical spectroscopy in the region between 300 nm and 10 mum. Two-dimensional imaging of chemical constituents makes this a very attractive and powerful new approach. In this paper we show SNOM results obtained in several geometrical configurations on boron clusters in silicon, Li clusters embedded in a LiF sample and BN growth on silicon. We also show some results on the wavelength dependence of the reflectivity (R) in the near infrared (IR) of biological cells in liquid environment with the observation of the local fluorescence. The SNOM images revealed features that were not present in the corresponding shear-force (SF) images and which were due to localized changes in the bulk properties of the sample. The size of the smallest detected features clearly demonstrated that near-field conditions were reached both in the visible and infrared region. (C) 2004 Elsevier B.V. All rights reserved.

Spatial distribution of InGaN photoluminescence (PL) at room temperature has been examined by observation through an illumination-transmission mode scanning near-field optical microscope (SNOM). The near-field PL mapping revealed a disuniform pattern of sharp or blunt emission peaks from few hundreds of nanometer extension to the micrometer scale range. The peaks’ average amplitude size and distances from neighboring peaks have been measured in a large number of experiments for three different samples at dissimilar indium doses, and their results compared. A general trend has been found and the influence of indium concentration is shown in a final plot. We describe the experimental approach adopted and present full details on the results obtained. Data were gathered from more than 100 different measurements; low-cost optical SNOM nanoprobes were originally fabricated and we briefly explain the fabrication procedure.

We demonstrated a novel application of a microfabricated force-sensing cantilever with a lead zirconate titanate (PZT) thin film as an integrated deflection sensor for a dynamic-mode atomic force microscope (AFM) combined with a scanning near-field optical microscope (SNOM). This experimental setup was also applied to a Kelvin-probe force microscope (KFM) for the investigation of local electrical properties. A frequency modulation (FM) detection method was used for enhancing the detection sensitivity of electrostatic forces between a probe tip and a sample. Local optical properties of a PbTiO3 single crystal were investigated using the conductive PZT cantilever as an AFM/SNOM probe. Furthermore, studies on local optical and electrical properties of ferroelectric copolymer films were also presented.

Optical writing and subsequent optical reading of sub-micron size features has been obtained at room temperature on a spin-coated film of polymethecrylate added with azobenzene mesogenic side groups (PMA4), by means of scanning near-field optical microscopy (SNOM). Illumination with blue or UV light through the SNOM aperture induces conformational transitions in the side units, obtaining their orientation in a localized region. Optical writing and topographic reading with subwavelength resolution have been demonstrated. The pure optical readback is obtained by laser light at 690nm through the aperture, in the polarization-modulation mode that provides sensitivity to dichroism and birefringence. Equally spaced lines have been written and subsequently imaged, presenting about one micron width in the birefringence image and about 600nm width in the scattering optical image. Local erasure of optical information can be obtained by using green light at 543nm with modulated polarization through the SNOM tip, in order to destroy the molecular alignment.

We demonstrated applications of a microfabricated cantilever with a lead zirconate titanate (PZT) piezoelectric thin film as an integrated deflection sensor to dynamic-mode atomic force microscopy (AFM) and to the related techniques including scanning near-field optical microscopy (SNOM) and Kelvin force microscopy (KFM). In the SNOM measurement, the evanescent light scattered by the tip apex was transmitted through the pyramidal hollow tip of the cantilever and it was detected by a photodetector placed in a confocal arrangement. Furthermore, local surface potential of a ferroelectric film was mapped by KFM using the frequency modulation (FM) detection method. Local poled ferroelectric domains made by the AFM tip were imaged by both SNOM and KFM.

A perylene-acetonitrile solution with TBAP (tetra-n-butylammonium perchlorate) electrocrystallizes on the electrode surface, under opportune conditions. It forms particular needle-like micro-crystals that have been studied recently for their peculiar electrical and optical properties and for the fundamental processes involved in the electron transfer responsible for the electrocrystallization. These intriguing structures present various fractal-like morphological organizations and diverse crystal shapes on the same deposition process. Up to now these formations have been studied optically by conventional standard microscopy. We introduce here a novel methodology to collect information on the actual orientation and crystal structure by a near field optical setup with originally fabricated probes. We performed, for the first time on these samples, near field fluorescence imaging showing evidence that the perylene aggregations actually have a distinct optical orientation.

Polymer liquid crystals with a photosensitive azobenzene side chain (azo-scPLC) are interesting materials because of their potential in optical switching and high density optical data storage applications. By illumination with blue linearly polarized light, the azobenzene chromophores undergo repeated trans-cis-trans isomerization cycles, resulting in reorientation of the side chains perpendicular to the electric field direction. We investigate the structural effects due to molecular reorientation in azo-scPLC on the scale of 10-100 nm by using a scanning near-field optical microscope (SNOM). We have selected a SNOM contrast mechanism suitable for domain discrimination by modulating the polarization at the input of the SNOM fiber probe and measuring the sample response with a lock-in technique, since the SNOM optical signal is polarization dependent. We image topographic and optical spontaneous structures of a Langmuir-Schaeffer multilayer of azo-scPLC and photoinduced micron-size patterns previously crea...