Michel Spajer

External and internal reflection near field microscopy: experiments and results.

Two configurations of a scanning near field optical microscope working in reflection are presented. Results exhibiting nanometric resolution are given and discussed.

Model for reflection near field optical microscopy

We discuss a model that describes the optical interactions between a dielectric tip and a surface exhibiting roughness of subwavelength size (infinite tracks). Such a model gives new insight into the resolution achievable by scanning near field optical microscopy. The dielectric tip is schematized as a cone whose extremity reduces to a small sphere acting as a dipolar scattering center, allowing separation of the contributions from the near field lying at the air-sample interface of other long range terms associated with the progressive waves coming from the surface. It is shown that because of its fast spatial dependence, the near field detected by the tip contains subwavelength features of the object. Relationships with preliminary experiments are discussed.

Reflection scanning near-field optical microscopy (R-SNOM) in constant height mode with a dielectric probe Image interpretation and resolution for high topographic variations

Abstract The understanding of the correlation between the near-field images that are recorded by scanning near-field optical microscopy (SNOM) and the local optical properties of the sample surface (topography, index, etc.) is a condition for the development of such microscopes. The aim of this paper is to show that the “constant height imaging” (CHI) mode provides useful near-field characterizations, even in case of high-relief samples. Actually, the CHI near-field signal is free from perturbations brought by usual feedback regulation systems. Furthermore, we show a comparison between experimental and theoretical data to explain near-field image formation. Finally, we develop a specific method based on the Fourier spectral analysis to characterize the experimental SNOM setup working in CHI mode.

Image resolution in reflection scanning near-field optical microscopy using shear-force feedback: characterization with a spline and Fourier spectrum

Scanning near-field optical microscopes (SNOMs) actually lead to nanometric lateral resolution. A combination with shear-force feedback is sometimes used to keep the SNOM tip at a constant force from the sample. However, resolutions in shear-force and optical data are different. An estimation of both resolutions is important for characterizing the capabilities of such systems. The basic principle of the measurement is to compare a spline-fitted logarithm of the power spectra calculated with the optical image with that of the shear force image in which resolution is determined a priori. Quantitative results are given in the case of periodic or untested sample and simulated data. Moreover the accuracy and the stability of the method are discussed.

Near-field probing control of optical propagation in bidimensional guiding mesostructures

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.

Spatially resolved study of Schottkey barriers

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.

Scanning local probe interferometer and reflectometer: application to very low relief objects

For the requirements of nanometrology, a new configuration of scanning interferometric profilometer, using a tapered fiber as emitting and detecting local probe, has been recently developed. The very large versatility allows a classical detection in far field, as well as a superresolution in near-field, for both transparent or nontransparent samples.

Near‐Field Optical Microscopy and Optical Tunneling Detection

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.

All-fiber heterodyne interferometer for vibration measurements in audible frequency range

The calibration of the novel laser heterodyne interferometry system for measurement of vibrations of small amplitude in the audible frequency range is described. A frequency-shifted reference beam is compared with an unshifted test beam that is phase modulated by a vibrating surface. Vibration displacements down 10 nm in the frequency range from 150 Hz to 10 KHz are measured. The system is ideally suited for biological movement analysis, for example, the acoustic emission evaluation from human cochlea excited by electrical stimuli.

SCANNING TUNNELING OPTICAL MICROSCOPY (STOM) USING A STYLUS SENSOR APPLICATION TO TOPOGRAPHY ANALYSIS OF GUIDING SURFACES

For overpassing the classical limit of resolution in optical microscopy, it is necessary to detect the diffracted light from small objects in the near field and not in the far field as in classical microscopy. A particular case is the detection of the evanescent field lying on the surface of a guiding structure. These surface waves interact with the object details and then can be used for determining the topography of the object. The chief problem is the detection because the light beam is confined on the object surface. A solution consists of frustrating the evanescent field by means of a dielectric probe. The conversion of the in-homogeneous waves into homogeneous ones is fundamentally similar to the electronic tunneling effect. Subwavelength resolution can be obtained by placing a suitable optical stylus connected to an optical fibre near the surface. A xyz piezo-electric micropositioning system allows then to scan the object surface under test. A microscope exploiting this principle has been built. Preliminary experimental results are presented and discussed.