Probing photonic and optoelectronic structures by Apertureless Scanning Near-Field Optical Microscopy

Advanced active polymer probe for near-field optics

We report on a novel, to the best of our knowledge, active probe for scanning near-field optical microscopy (SNOM). A fluorescent nanosphere, acting as the secondary source, is grafted in an electrostatic manner at the apex of a polymer tip integrated into the extremity of an optical fiber. Thanks to the high photostability and sensitivity of the secondary source, the near-field interaction with a gold nanocube is investigated. It is shown that the spatial resolution is well defined by the size of the fluorescent nanosphere. The polarization-dependent near-field images, which are consistent with the simulation, are ascribed to the local excitation rate enhancement. Meanwhile, measurement of the distance-dependent fluorescence lifetime of the nanosphere provides strong evidence that the local density of states is modified so that extra information on nano-emitters can be extracted during near-field scanning. This advanced active probe can thus potentially broaden the range of applications to include nanoscale thermal imaging, biochemical sensors, and the manipulation of nanoparticles.

Note: Multiscale scanning probe microscopy

Combining the nanoscopic and macroscopic worlds is a serious challenge common to numerous scientific fields, from physics to biology. In this paper, we demonstrate nanometric resolution over a millimeter range by means of atomic-force microscopy using metrological stage. Nanometric repeatability and millimeter range open up the possibility of probing components and materials combining multiscale properties i.e., engineered nanomaterials. Multiscale probing is not limited to atomic-force microscopy and can be extended to any type of scanning probe technique in nanotechnology, including piezoforce microscopy, electrostatic-force microscopy, and scanning near-field optical microscopy.

Full simulations of the apertureless scanning near field optical microscopy signal: achievable resolution and contrast

We simulate apertureless near-field optical imaging and obtain phase and amplitude scans of structured substrates for elastic scattering. The solution of the three-dimensional Maxwell equations does not involve approximations and we include large tips and substrates, strong interaction, interferometric detection and demodulation at higher harmonics. Such modeling represents a significant step towards quantitative simulations and offers the attractive possibility to study the individual influence of each relevant experimental parameter. We typically obtain highly localized signatures of the interaction of the tip with gold inclusions, superposed on a slowly varying background signal. The relative importance of both contributions and the achievable lateral resolution are strongly dependent on the geometry and scanning conditions. The simulations show sensitivity mostly to the first nanometers of the sample and underline the importance of scanning near the sample and being careful with mechanical anharmonicities on the tip oscillation. They also help to determine the influence of oscillation amplitude and demodulation harmonic.

Phase sensitive optical near-field mapping using frequency-shifted laser optical feedback interferometry

The use of laser optical feedback Imaging (LOFI) for scattering-type scanning near-field optical microscopy (sSNOM) is proposed and investigated. We implement this sensitive imaging method by combining a sSNOM with optical heterodyne interferometry and the dynamic properties of a B class laser source which is here used both as source and detector. Compared with previous near field optical heterodyne experiments, this detection scheme provides an optical amplification that is several orders of magnitude higher, while keeping a low noise phase-sensitive detection. Successful demonstration of this complex field imaging technique is done on Silicon on Insulator (SOI) optical waveguides revealing phase singularities and directional leakage.

Localized current injection and submicron organic light-emitting device on a pyramidal atomic force microscopy tip

An organic light-emitting device was fabricated on a commercial atomic force microscopy (AFM) probe having a pyramidal tip by a lithography-free vacuum thermal evaporation (VTE) process. The line-of-sight molecular transport characteristic of VTE results in controlled thickness variation across the nonplanar substrate, such that localized current injection occurs at the tip region. Furthermore, the high curvature of the AFM tip vertex concentrates the electric field, causing highly localized bipolar charge injection, accompanied by photon emission from a region less than a micrometer across. This light source exhibits a range of features potentially attractive for applications such as probe-based optical microscopy, nanoscale light sensing, and chemical detection.

Enlarged atomic force microscopy scanning scope: novel sample-holder device with millimeter range

We propose a homemade sample-holder unit used for nanopositionning in two dimensions with a millimeter traveling range. For each displacement axis, the system includes a long range traveling 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. For this we chose to characterize highly integrated optical structures. For this purpose, the sample holder was integrated into an atomic force microscope. A millimeter scale topographical image demonstrates the overall performances of the combined system.