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International audience; We report on two novel ways for patterning Lithium Niobate (LN) at submicronic scale by means of focused ion beam (FIB) bombardment. The first method consists of direct FIB milling on LiNbO3 and the second one is a combination of FIB milling on a deposited metallic layer and subsequent RIE (Reactive Ion Etching) etching. FIB images show in both cases homogeneous structures with well reproduced periodicity. These methods open the way to the fabrication of photonic crystals on LiNbO3 substrates.

Radially polarized beams are beams for which the electric vector is radially distributed along the beam axis. Such beams are interesting for applications in which a total symmetry of the electric field is required. In this paper we propose an all-fiber method allowing the generation of radially, azimuthally, and hybrid polarized light beams in a rapid and simple way.

Scanning near-field optical microscopy is used for analyzing both the interaction of light with mesostructures and the capability of wave transfer between two macrowaveguides coupled by a matrix of periodic mesostructures. A spectral analysis shows the influence of the wavelength in such a configuration.

The study of semiconductor interfaces and of solid interfaces in general requires novel instrument capable to investigate the lateral fluctuations of properties on a microscopic scale. We present the first result of a major effort in that framework, whose main objective is the exploitation of the unique characteristics of free electron laser (FEL) infrared sources. The background was provided by our previous development of FEL-based techniques to measure interface barriers with high accuracy and reliability. Quite recently, we were able to implement similar investigations with high lateral resolution. The key elements were the use of a small-tip optics fiber and its coupling with a scanning module; in this way, we achieved and verified the condition of near-field microscopy including a lateral resolution much below the wavelength value. Our discussion includes a presentation of the first scanning near-field optical microscopy (SNOM) images obtained with an FEL and data on small and microscopic-scale fluctuations of semiconductor interface barriers. The likely development of this exciting new field will also be discussed, in particular considering the new proposals for powerful FELs in the low-wavelength spectral range.

An optical device was constructed to collect near-field Raman spectra (NFRS) and far-field scattering Raman spectra simultaneously on the same sasample area. In Raman applications where the studied samples do not enjoy any advantages of resonance effects, the nanoprobe may be used only as a nanodetector in order to avoid damage of the tip by the necessary laser powers. The silicon-based samples, which are either calibrated grid or a single crystal, were studied by NFRS and conventional scattering Raman spectroscopy. The near-field Raman signal of silicon is divided by at least four when the tip–silicon substrate distance is separated by a 100 nm layer of oxide. Moreover, between the NFR spectrum and the far-field spectrum, on the single crystal, a shift of about 10 cm−1 is displayed. Some interpretations are discussed. These experiments confirm the potential of the NFRS already emphasized previously in the literature. Copyright © 1999 John Wiley & Sons, Ltd.

Gratings can be considered as resonant structures in near-field. The enhancement of the intensity recorded by Scanning Near-Field Optical Microscopes (SNOM) is due to interferences in relation with the ratio of the wavelength to the product of the optical index by the period of the grating. We discuss the effect of this ratio (in the range 0.9, 1.1) on the intensity patterns. The influence of the polarization on near-field data is analyzed in both theoretical computations and experimental result.

This contribution presents an application of scanning near-field optical microscopy to the characterization of semi-conductors. It is based on the photocurrent mapping of a patterned Au/GaAs structure (Schottky barrier) under local illumination by the nanosource. The results obtained with different wavelengths, metallized or dielectric probes and different bias voltages exhibit photocurrent variations independent of the topography and induced by interface defects. Finally, from this study of a patterned planar structure, we propose a method to determine the mean free path of the charge carriers in the volume.

In this paper, we report a series of two-dimensional computerized simulations to gain more insight in the mechanisms responsible for near-field optical nanolithography (NFONL). Several significant factors are considered successively, e.g., the kind of tip used to illuminate the photosensitive sample (purely dielectric or coated tips), and the polarization of the incident electromagnetic field. A comparative study of the near fields generated by bulk dielectric and metallized tips is important to determine their relative capability as efficient tools for nanoindentation. In the same manner, the role of the tip–sample spacing during the exposure of the sample has also to be assessed to get a better control of the resulting nanoindentation patterns. Finally, a simultaneous study of both s- and p-polarizations is mandatory if we want to interpret recent experimental data issued from standard three-dimensional devices. With the help of these simulations, we explain some typical effects encountered during nanoindentation experiments realized with a reflection SNOM architecture.

We report a microscopic study of the Au/5 Angstrom SiNx/GaAs Schottky barrier based on scanning near-field optical microscopy. Photocurrent yield microimages taken at different photon energies reveal non-topographic features. Taking into account their dependence on photon energy and bias, such features are consistent with lateral variations of the local density of states related to defects. The results, therefore, confirm that lateral variations must be considered when analyzing semiconductor interfaces and of the corresponding devices. (C) 1998 Elsevier Science B.V.

We studied the Pt n-GaP buried Schottky junction by several spatially resolved techniques to correlate the chemical inhomogeneities of the interface with the spatial variations of the diode transport properties. The recombination rate fluctuations and small spatial variations (3–8 meV) of the Schottky barrier height were correlated with the local stoichiometry of the bare GaP surface and of the fully formed junction. We discovered regions with local segregation of metallic gallium. In these regions we measured a Schottky barrier height only 4 meV lower than in the stoichiometric areas. On the contrary these zones presented a more important electron-hole recombination rate.

This paper presents the preliminary results of the use of near-field optical microscopy for the observation of latent images in photoresists. It is shown that the refractive index change between exposed and unexposed regions is detected with a good contrast not always related to topography. Sub half-wavelength resolution capability is demonstrated.

Near field reflection imaging on non-developed photoresists is achieved using a dielectric probe. Preliminary results demonstrate a subwavelength resolution uncorrelated with topographic image and a contrast related to the index change integrated on the layer thickness.

Our aim is to transpose the polarization control by mechanical stress, usually applied to single-mode fibers, to the(TM01,TE01,HEev21,HEod21) annular mode family. Nevertheless, the quasi-degeneracy of these four modes makes the situation more complex than with the fundamental mode HE11 . We propose a simple device based on periodic perturbation and mode coupling to produce the radially polarized TM01 mode or at least one of the four modes at the extremity of an arbitrarily long fiber, the conversion to TM01 mode being achievable by classical crystalline plates. OPTICS LETTERS, ISSN : 0146-9592, DOI : 10.1364/OL.36.000205, Issue : 2, Volume : 36, pp. 205-207, 15 January 2011.

A new scanning profilometer using a tapered fiber and a detection developed for near field microscopy is described. Results obtained with probes ended by a microlens or a conical tip are presented and compared to images given by classical microscopes.

Near-field fluorescence spectra with subdiffraction limit spatial resolution have been taken in the proximity of mitochondrial membrane inside breast adenocarcinoma cells (MCF7) treated with the fluorescent dye (JC-1) by using a scanning near-field optical microscope coupled with a confocal laser microspectrofluorometer. The probe–sample distance control is based on a piezoelectric bimorph shear force sensor having a static spring constant k=5 μN/nm and a quality factor Q=40 in a physiological medium of viscosity η=1.0 cp. The sensitivity of the force sensor has been tested by imaging a MCF7 cell surface.

A near-field optical device has been developed to collect sum frequency signal, generated in an AsGa single crystal sample by two pulsed lasers, one fixed at a wavelength of 532 nm and the other tunable in midinfrared. The sum frequency signal was collected with an uncoated silica tip. When the tip sample distance was increased, a strong decrease of the collected sum frequency signal was observed: the signal was divided by 2 for an increase of about 100 nm of the distance between the nanoprobe end and the sample surface. Without demonstrating submicronic lateral spatial resolution, this letter is, however, a first step towards a microscopic device of sum frequency generation spectroscopy.

A new nonoptical shear force detection for scanning near-field optical microscopes is proposed in this article. Its main characteristic is a simple and fast tip replacement. The probe is mechanically in contact with a piezoelectric plate of a homemade tuning fork, ensuring a direct coupling and avoiding the fiber tip gluing.

International audience; We propose a method for producing a conical beam based on the lateral refraction of the TM01 mode from a two-mode fiber after chemical etching of the cladding, and for controlling its radial polarization. The whole power of the guided mode is transferred to the refracted beam with low diffraction. Polarization control by a series of azimuthal detectors and a stress controller affords the transmission of a stabilized radial polarization through an optical fiber. A solid component usable for many applications has been obtained.

International audience; Acoustic field distribution was determined in HIFU sonoreactors as well as localization of cavitation activity by crossing different techniques: modeling, hydrophone measurements, laser tomography and SCL measurements. Particular care was taken with quantification of this last technique by pixels or photon counting. Cavitation bubbles generated by HIFU are mainly located on the outer layer of the propagation cone in the post-focal zone. Greatest acoustic activity is not located at the geometrical focal, but corresponds to a high concentration of bubbles zone. On the contrary, the main sonochemical activity shifts slightly toward the transducer, whereas quenching of inertial cavitation is observed directly at the focal. Finally, SCL thresholds have been determined.

We report on a heterodyne interferometric scanning near-field optical microscope developed for characterizing, at the nanometric scale, refractive index variations in thin films. An optical lateral resolution of 80 nm (lambda/19) and a precision smaller than 10(-4) on the refractive index difference have been achieved. This setup is suitable for a wide set of thin films, ranging from periodic to heterogeneous samples, and turns out to be a very promising tool for determining the optical homogeneity of thin films developed for nanophotonics applications. (C) 2009 American Institute of Physics. [doi:10.1063/1.3226660]

International audience; This work addresses the use of fixed-angle laser reflectometry to follow in situ the deposition of self-assembled polyelectrolyte films in a large domain of thickness. It is shown theoretically and illustrated experimentally that the reflectometric output can be interpreted in terms of refractive index and thickness way above the usual range which covers the earlier deposition steps of the polymers (i.e., 30-50 layers, depending on the film composition). Thick films containing up to 320 deposition steps (160 bilayers) were made in the reflectometric cell with the polymer pair poly(allylamine, hydrochloride) and poly(styrene sulfonate) on a silica substrate. They were imaged with AFM, and their thickness was measured using the focused ion beam (FIB) technique. In the course of construction, the reflectometric data started to alternate more or less regularly between positive and negative values, exhibiting absolute values at the extrema which decreased progressively. This phenomenon was coherent with simulated data, once the diffusion of the incident beam and the change of refractive index were taken into account. The phenomenon gives an opportunity to evaluate the composition and the mean thickness of the film during the growth, which is confirmed by comparison with the FIB measurements.

The thickness evolution of multilayer film is investigated by focused ion beam (FIB) in the domain of polymer multilayers. This method, currently used in the modification and the characterization of integrated circuits, proves it is possible to determine the polymer film thickness. Sample cutting and its observation of the cross-section are performed in the FIB without leaving the vacuum chamber. Two main conclusions can be drawn: (1) the roughness of the film increases with the number of layer deposit, (2) the film growth changes from nonlinear (called exponential) to linear beyond 300 nm (70 layers).

International audience

A technique for controlling the tip–sample distance in near-field optical microscopes is presented. It consists of mechanically exciting a fiber tip inserted without any adhesive between the two prongs of a high Q-piezoelectric tuning fork. The detection of the shear forces is classically achieved by measuring the decrease of the dithering amplitude when the tip approaches the surface. This simple setup greatly simplifies tip replacement and its resonance frequency tuning.

International audience

International audience

The combination of internal photoemission and near‐field optics is proposed as a generally applicable approach to study the lateral variations of solid interface properties such as energy barriers and electron‐hole recombination rates. A successful test on Pt–GaP is described in which topographic and nontopographic phenomena are revealed, in particular recombination rate variations and small lateral changes of the Schottky barrier height.

A new type of electrochemical cell has been developed for use in electrochemical, chemical and biological applications. Using a platinum microelectrode as working electrode, this cell incorporates a silver microelectrode as reference electrode. These microelectrodes, whose area is equal to 1 μm 2 , were fabricated using photolithography, sputtering, and focused ion beam (FIB) technologies since these micro-fabrication techniques allow us to develop miniaturized electrochemical cells useful either for nanoelectrochemistry or biosensors applications. In this study, we show it is possible to coat a surface by chemical or biological compounds by immersing the microelectrodes in a solution, then setting a difference of potential between the two microelectrodes of the cell. For example, we used this miniaturized cell to realize the electrochemical polymerization of aniline into polyaniline to show that this electrochemical cell is efficient to coat a surface with a thin film of polymer.

Micromachining technology has potential for fabrication of precision-defined integrated optic (IO) circuits and offers easy alignment procedures for optical fibers, reducing packaging costs. The main difficulties in fiber sensing technologies are optical fiber alignment requirements, high temperature and vibration effects sensitivity, and phase noise. An alternative is the use of MEMS/MOEMS to approach these problems, combining fiber-optic technology and silicon micromachining. Integrated sensors, when linked by optical fibers, can provide EMI immunity and isolation from high voltage circuits. Detection of displacements of cantilever beams, microbridges, or membranes is used to sense the physical parameter, converting mechanical displacement to a change in optical intensity, and serves as the basis for sensors, since many physical parameters (temperature, pressure, force, acceleration) can be converted to a displacement or strain. The interest in silicon micromachining is also demonstrated in coupling of optical fibers to optoelectronic devices by passive alignment of fiber on a V-groove shaped silicon microbench. Finally, highly reproducible processes such as focused ion beam (FIB) may fabricate near-field optical sensors with nanometer apertures at the apex of tapered fibers. In this paper, a number of sensors are discussed in order to analyse how silicon micromachining contributes to fiber optic sensor technology.

An optical fibre ending in a trihedral tip is proposed as a convenient probe for reflection near-field optical microscopy in emission/collection mode. Its shape is obtained by ion milling. A first example of manufacturing and numerical models using the bi-dimensional FDTD method is presented. It confirms the strong influence of the facet angle on the intensity reflected by the probe, which is predicted by a rough analysis. This method can help us to optimize the 'reflection probe' by reducing this offset signal.

We report new experimental results, and their theoretical analysis, on the mechanisms that control light transfer between two integrated waveguides connected by two-dimensional matrices of dielectric pillars. The optical properties of the system are analysed from the well-established formalism of classical field susceptibilities (Green dyadic functions). We apply this scheme to investigate the optical properties of two-dimensional arrays connected to two integrated waveguides. Comparisons with current experimental work based on near-field optical probing are provided together with a spectral analysis of the phenomenon.

The present paper deals with the experimental measurement of temperature along various shapes of fiber tips used as near-field optical microscope probes. An ultra-small thermoelectric couple makes it possible to detect the tip temperature as far as the junction dimension remains smaller than the local investigated area. The couple is a 0.5 μ m Pt and Pt–Rh 10 % welded wires, whose dynamic and dimensional characteristics allow the investigation of the thermal behaviors of tapers under steady-state and periodic excitation modes (bandwidth near 1 kHz). Temperature profiles along these fiber tips (up to 400 μ m from the apex) are shown and discussed. Confirming some authors' results, dramatic temperature increases due to an internal heating can occur for some configurations. Such temperatures can play a key role in the imaging process, because of the resulting behaviors of the apex, mainly due to its thermal expansion. Indeed, variation of the aperture diameter and thermoelastic interaction with the sample surface could explain some artefacts in the resulting images.

This contribution presents an application of scanning nearfield microscopy to the char-acterization of semiconductors. We have studied the planar homogeneity of a Au/GaAs Schottky barrier using a local illumination by a nanosource with various wavelengths.One of the main results is the interface defaults revealed by the photocurrent mapping at ) = 1.33im. 1. Introduction As the technology of semi-conductors uses structures of subwavelength dimension, the Scanning Near Field Optical Microscope (SNOM) appears as a powerful mean of investigation to controltheir real working mode and to detect inhomogeneities. Spectacular results were obtained withlocal spectroscopy of quantum structures,' field mapping in guiding structures2'3 and in lasercavities, mapping of the induced photocurrent... In this last application, which is an extensionof far field methods OBIC (optical beam induced current),4 the focused laser beam is replacedby a nanosource. The authors stress on the vertical analysis of the layers5 or on the lateral

We studied the fully-formed (80 angstroms) Pt/GaP and (140 angstroms) Au/GaAs interfaces by scanning near-field optics microscopy, internal photoemission, atomic force microscopy, and by x-ray photoemission electron microscopy. These complementary techniques enabled us to correlate the spatial variations of the diodes transport properties with the chemical and topographic inhomogeneities of the buried metal-semiconductor interfaces.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Reflection near field microscopy is potentially more accurate and efficient than STOM, its advantage beeing a localized illumination of the surface. Its working in far field and near field mode is described and the experimental z-curve is analyzed. A solution for partially solving the inherent problem of S/N ratio is presented. It uses electronic and numerical z-derivation of the signal.

By exploring the surface of an illuminated object at a very short distance by means of a subwavelength detector, it is possible to reconstruct images whose resolution is beyond the diffraction limit. This opportunity due to near field properties can be explained in terms of non radiative field detection that is of optical tunneling effect. We present some recent results obtained by using two different illumination‐detection configurations. The first one using internal reflection allows to analyze the surface of transparent objects whereas the second one using the same tip as subwavelength emittor and detector is suitable for reflecting objects.

The scanning tunneling optical microscope (SNOM, STOM, PSTM, etc.) is the equivalent of the electron scanning tunneling microscope in the electromagnetic domain. Although it was born at the same time, its actual development is more recent. Here, some new results obtained with the version working in total reflection (STOM/PSTM) are reported. A grating of a periodicity of 417 nm and a thickness of 5 nm have been imaged both in TM and TE modes. It is first noted that the optical image is well resolved. Furthermore, the difference of behavior of the field versus the polarization of the incident light has been shown. More precisely, the TM mode seems to be highly sensitive to small index and topography variations due to surface contaminants. Such effects are generally not imaged by atomic force microscopy working in attractive mode, because they affect the surface topography slightly. The SNOM could be thus a very powerful tool for detecting pollutants over the surface of objects like glasses, lenses, gratings...

Le deviateur du tenseur des contraintes peut etre determine au moyen des techniques photoelasticimetriques classiques. La composante isotrope s'obtient par interferometrie holographique soit en mesurant les variations relatives d'epaisseur (modeles bidimensionnels) soit en faisant apparaitre les variations absolues d'indice (methode du ‘figeage’ des contraintes). Dans les deux cas les perturbations, introduites par les franges isochromes et liees aux effets de birefringence, sont eliminees par une double traversee de l'objet, le faisceau lumineux subissant une rotation de 90 degres de sa polarisation avant d'effectuer le trajet retour. L'acces a la somme des contraintes principales par des measures ellipsometriques fait l'objet d'un developpement particulier; la relation, C1+2C2=0, entre les constantes photoeastiques absolues des materiaux ‘figeables’, a ete confirmee dans le cas particulier du materiau PLM4B Photolastic (Vishay).

The present paper analyses the factors affecting the quality of the moire fringes for an arbitrary displacement and deformation of the object surface. Methods for the generation of auxiliary fringes are considered and their localisation is investigated. The physical significance of speckle displacement, both in the image plane and in the pupil plane, is pointed out.

Interference of the fundamental mode with LP11 and LP02 are used to separate temperature variation from longitudinal strain in a fibre sensor; the measurement technique is fringe counting. Polarisation fading is overcome by triple detection through different analysers.

The retraction of the silicone elastomers used to make teeth impressions in odontology bears on the sensitivity of the moulding process. An optical study of this retraction has been carried out using interferometry in monochromatic light - holographic interferometry - and in white light - channelled spectrum method. The diversity of the results obtained evinces the influence of experimental parameters such as temperature, hygrometry and conditions of impression and removal.

Various methods for the measurement of hydrostatic stress i.e. the isotropic component of the stress tensor, are presented. All these methods lead to a whole-field visualization. In two dimensional problems, the hydrostatic stress is obtained by the measurement of the relative variation of thickness, caused by loading the model ; by using the technique of double exposure holographic interferometry. The birefringence effects are eliminated by making the object beam to pass through the model, and in-between the two passes, the beam is subjected to a 900 rotation of its plane of polarization. In the case of three-Aimensional models, the method is based on the observation of the variations in the absolute index of refraction. The frozen-stress technique requires the use of those photoelastic materials which remain compressible at the "freezing" temperature ; but unfortunately, they are unavailable at present. Therefore, a non-destructive optical-slicing method is proposed and it is hoped that it shall give the required information concerning the hydrostatic stress. This method consists of an interferometric comparison of the two superimposed speckle patterns, each scattered from two neighbairing optically isolated light sheets. Further, the measurement of the in-plane strain can be carried out using either holographic or speckle pattern interferometry ; the precision is found to be the same in both cases.© (1978) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The paper deals with a problem of deformation applied to dentistry when making imprints with precision impression materials such as silicone elastomers. A study of their dimensional variations has been carried out through (i) holographic interferonstry in laser light, (ii) interferometry in white light based upon the channelled spectrum phenomenon. Both high and low-bodied elastomers have been tested. The results indicate the influence of the thickness of the sample on the speed of retraction during the polymerization of the material. Furthermore, external parameters such as the temperature and the hygrometric degree have to be taken into account when making accurate imprints.

A method that achieves automatic measurements of the orthogonal components of the motion of optically rough surfaces is described. An optical set-un that implements a speckle rotation is used to extract the components of 2-D displacements, which are obtained from simultaneous data recording performed by a single 1-D CCD line. A temporal analysis of speckle patterns related with a given inspected area of a moving structure is then possible. The movement trajectory is reconstructed. The principle of the method and the experimental set-up are described. Experimental results are shown with a specific application to the deformations of a video film structure under directional traction and dynamic analysis of thermal deformations of mechanical parts.

We used a combination of internal photoemission and of near-field optical microscopy (SNOM) to study the lateral Variations in solid interface properties such as energy barriers and electron-hole recombination. Ln particular we investigated the fully formed Pt-GaP, Au-GaAs, Au-SiNx-GaAs and PtSi-Si Schottky barriers. Our approach enabled us to measure large lateral variations in the photocurrent with spatial resolution on the nanometric scale. Due to the ability of SNOM to supply parallel topographic information, we observed photocurrent variations from zone to zone that only correlated in a few cases with local variations in surface morphology. We assigned the uncorrelated fluctuations to local variations in the interface stoichiometry, the presence of interface states induced by the metallic overlayer and to defect states at the junction. Furthermore, by tuning the photon energy and applied bias we were able to measure the surface distribution of the diffusion length.

Interference between the LP(01) and LP(02) modes is used to measure fiber elongation. We present a passive phase-detection technique that uses a mask in the far field of the output beam and spatial filters in the image of the fiber end face, giving a linear response. Experimental results show a precision of about 3% of one period, which corresponds to a 4-microm elongation.