Near-Field Scanning Optical Microscope Combined with Digital Holography for Three-Dimensional Electromagnetic Field Reconstruction

International audienceNear-field scanning optical microscopy (NSOM) has proven to be a very powerful imaging technique that allows overcoming the diffraction limit and obtaining information on a scale much smaller than what can be achieved by classical optical imaging techniques. This is achieved using nanosized probes that are placed in close proximity to the sample surface, and thus allow the detection of evanescent waves that contain important information about the properties of the sample on a subwavelength scale. In particular, some aperture-based probes use a nanometer-sized hole to locally illuminate the sample. The far-field radiation of such probes is essential to their imaging properties, but cannot be easily estimated since it highly depends on the environment with which it interacts. In this chapter, we tackle this problem by introducing a microscopy method based on full-field off-axis digital holography that allows us to study in details the three-dimensional electromagnetic field scattered by a NSOM probe in different environments. We start by describing the NSOM and holography techniques independently, and continue by highlighting the advantage of combining both methods. We present a comparative study of the reconstructed light from a NSOM tip located in free space or coupled to transparent and plasmonic media. While far-field methods, such as back focal plane imaging, can be used to infer the directionality of angular radiation patterns, the advantage of our technique is that a single hologram contains information on both the amplitude and phase of the scattered light, allowing to reverse numerically the propagation of the electromagnetic field towards the source. We also present Finite Difference Time Domain (FDTD) simulations to model the radiation of the NSOM tip as a superposition of a magnetic and an electric dipole. We finally propose some promising applications that could be performed with this combined NSOM-holography technique

Ring grating-nanoprism structure for efficient focusing of surface plasmon polaritons

This work aims to study light-matter interaction at the nanoscale by integrating emitters with plasmonic structures. Our proposed structure consists of metallic nanoprisms in the center of ring diffraction gratings. Surface plasmon polaritons (SPPs) are generated by the ring grating which propagate and get focused on the nanoprism tip forming an intense electromagnetic hotspot in the region. FDTD numerical simulations are done to calculate the optimized angle of incidence needed for SPP excitation by the ring grating. Sample fabrication and optical characterization methods are presented to study the coupling between generated SPPs and CdSe quantum dots placed in the center. FDTD simulations as well as experimental observations are done to study the electromagnetic hotspot at the tip of the ring gratingnanoprism structure. This work will be extended further to include the coupling between SPPs and emitters placed in the hotspot which leads to their photoluminescence and lifetime enhancement.Published versio

Chemoheteroepitaxy of 3C-SiC(111) on Si(111): Influence of Predeposited Ge on Structure and Composition

Secondary ion mass spectroscopy, Fourier transformed infrared spectroscopy, ellipsometry, reflection high energy diffraction and transmission electron microscopy are used to gain inside into the effect of Ge on the formation of ultrathin 3C-SiC layers on Si(111) substrates. Accompanying the experimental investigations with simulations it is found that the ultrathin single crystalline 3C-SiC layer is formed on top of a gradient Si1–x–yGexCy buffer layer due to a complex alloying and alloy decomposition processes promoted by carbon and germanium interdiffusion and SiC nucleation. This approach allows tuning residual stress at very early growth stages as well as the interface properties of the 3C-SiC/Si heterostructure. Useful yields of secondary ions of Ge in Si matrix and Si dimer are estimated