The effect of size on transitions between defect-induced magnetic phases in ZnO nanowires is investigated in a temperature range from 1.8 K to 300 K using calorimetric measurements of specific heat. The obtained results demonstrated interesting magnetic phenomena in unusual magnetic nanomaterials. At low temperatures, we observed isolated magnetic ions in nanowires of diameters 45-50 nm, and ferromagnetic phases in nanowires of diameters 85-100 nm. However, at higher temperatures, we observed multiple transitions between superparamagnetic phases in the thinner nanowires and multiple transitions between spin-glass phases in the thicker nanowires.
The Nb2CTx MXene was synthesized and optically characterized utilizing Photo-induced Force Microscopy (PiFM), a nanoscale imaging technique combining AFM topography mapping and infrared spectroscopy. In both bulk and single/few layered MXene flakes, absorption peaks were observed in the 770 - 1860 cm-1 investigated range. The local IR spectra is compared with broader Fourier-transform infrared (FTIR) and Raman spectroscopy to analyse the material composition. Our findings notably highlight the presence of a characteristic peaks related to surface functional group in both far-field and near-field measurement. The spectra also indicate a strong contribution of niobium oxide in the synthetized material.
We have developed a scattering-type microscope operating in the mid-IR range with a polarization analysis. The
experimental development and the operation of the microscope are described. The optical system can provide for each
pixel of the image a matrix similar to a Jones matrix. Examples of polarization resolved images obtained on a SiO2/Si
surface grating with a tungsten probe are shown and a high optical resolution is clearly demonstrated through the
imaging of submicron metallic lines.
KEYWORDS: Waveguides, Near field scanning optical microscopy, Near field optics, Brain-machine interfaces, Near field, Wave propagation, Silicon, Multimode interference devices, Silicon photonics, Light wave propagation
Optical devices based on SOI have been fabricated and tested for the last decade by using far field optics.
Alternatively, near-field scanning optical microscopes (NSOM) have the ability to reach unique optical resolution
by converting the evanescent waves into radiation waves that can be detected by conventional far field optics.
Thus, the aim of this paper is to show the most recent capabilities of the NSOM in a guided detection to probe
SOI-based structures. By using this simple yet powerful configuration, we can observe the propagation of the
light in Si-based devices and thus measure the propagation characteristics of the guided modes.
KEYWORDS: Waveguides, Near field optics, Plasmonics, Silicon, Near field scanning optical microscopy, Copper, Near field, Wave propagation, Light wave propagation, Atomic force microscopy
Plasmonic waveguiding structures have the ability to confine and propagate light over short distances, typically
less than a hundred micrometers. This short propagation length is the price that is paid for confining light to
dimensions on the order of a hundred of nanometers. With these scales in mind, several plasmonic devices can be
proposed (e.g. wavelength multiplexors) and some of them have been already demonstrated such as Y junctions
and directional couplers. Although the dimensions involved in such structures are below the diffraction limit,
large-scale optical characterization techniques, such as transmitted power, are still employed. In this contribution,
we present a characterization technique for the study of the guided modes in plasmonic gap waveguiding structures
that resolves subwavelength-scale features, as it is based on atomic force microscope and on near field scattering
optical microscope in guided detection.
We study both experimentally and numerically far-field radiation patterns of single metallic nanowires coupled
to weak confined optical waveguides. The radiation pattern resulting from the interaction of the nanowire and
the optical mode depends strongly on the mode properties (polarization and wavenumber) and on the antenna
properties (material and size). To investigate these phenomena we compare the electric far-field distributions
computed with different numerical methods (Green's tensor technique, rigourous coupled wave method, Fourier
modal method). We also compare simulated results to experimental measurements obtained over a large spectral
domain ranging from 400 nm to 1000 nm. This study should be useful for optimizing nanostructured photonic
circuits elements.
We developed a home-made sample-holder unit used for 2D nano-positioning with millimeter travelling ranges. For each
displacement axis, the system includes a long range travelling stage and a piezoelectric actuator for accurate positioning.
Specific electronics is integrated according to metrological considerations, enhancing the repeatability performances.
The aim of this work is to demonstrate that near-field microscopy at the scale of a chip is possible. We chose here to
characterize highly integrated optical structures. For this purpose, the sample-holder is integrated into an Atomic Force
Microscope in order to perform optical imaging. To demonstrate the overall performances, a millimeter scale optical
images have been realized.
KEYWORDS: Near field optics, Near field scanning optical microscopy, Waveguides, Heterodyning, Atomic force microscopy, Brain-machine interfaces, Silicon, Integrated optics, Dispersion, Wave propagation
This article presents recent advances in scattering-type near field optical scanning microscopy used as a powerful
characterization tool for integrated optics. By significant examples, it is shown that this specific probe microscopy based
on an Atomic Force Microscope setup with optical heterodyne detection functionalities allows for in situ quantitative
study of the complex field propagating in compact silicon on insulator photonic structures (single channel waveguides,
MMI splitters and microdisk resonators).
KEYWORDS: Actuators, Near field, Interferometers, Control systems, Mirrors, Heterodyning, Near field optics, Phase shifts, Electronic circuits, Optoelectronics
We report on a new high accuracy home-made sample holder for near field characterization of millimeter long wave guiding structures (Y junction, Multi Modes Interference coupler). The principle of near field characterization is based on an atomic force microscopy tip that is brought to the surface of the sample (in the near field zone) in order to coupled out a small amount of the light confined inside the wave guiding structures. Due to the size of the components, scans as long as a few millimeters are required to get an entire optical mapping of the structure [1]. With the commonly available equipments such a scan is performed by acquiring step by step more than 100 images for a 2 mm scan. The overlapping of the different images is time consuming and unsatisfactory unless a numerical stitching procedure based on topographical details is used. Effective refractive indexes are typically determined with a precision of 10-3 which could be further improved by increasing the millimeter scan resolution. The reason why successive images do not overlap is mainly due to the mechanical system supporting the sample. Actually, the nonlinearity of the actuator and the thermal expansion of the mechanical part prevent us to reach nanometric scale of repeatability on the positioning for micrometric range of displacements. In order to enable long range scans with nanometric repeatability and accuracy, we develop a specific mechanical system controlled by a heterodyne interferometric apparatus and a home-made high frequency electronic board [2]. The position of the sample is measured in real time with a resolution of 0.3 nm. The servo-loop allows to control the position of the sample with a repeatability of 1 nm (1σ) for a displacement of 1 mm. Furthermore our method is insensitive to the nonlinearity of the actuator.
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