Xavier Bouju

Coupled electromagnetic modes between a corrugated surface and a thin probe tip

A self‐consistent formalism is presented in order to determine the dispersion equation of the coupled electromagnetic modes between a dielectric probe tip of arbitrary shape and a rough surface. A microscopic picture of the matter is used for describing the dielectric response of the tip, and the coupling with the substrate is introduced from a dynamical matrix expressed in terms of propagators. Retardation effects may be included without formal difficulty through an appropriate response function describing the surface of the solid (local or nonlocal). An advantage of such a calculation lies in the possibility of simulating dielectric tips of arbitrary shape without introducing boundary conditions at the surface of the probe. Connection with atomic force microscopy and near field detection by local probe will be discussed.

Glass and silicon probes: A comparative theoretical study for near-field optical microscopy

Glass fibers, chemically etched at their extremities and covered with a thin metal coating, are often present in near-field optical microscopy. Such elongated systems can be used to either probe the evanescent components of the electromagnetic field at the surface of a sample, or locally couple this sample with optical evanescent waves. In this article, we analyze theoretically an alternative tip design made with a silicon core. This kind of probe could be very useful when infrared properties of a surface are to be investigated. The advantages of using such a material for near-field optical detection will be stressed and compared with the performances of a bulk glass fiber.

Theoretical study of the atomic-force-microscopy imaging process on the NaCl(001) surface

Based on a fully relaxed molecular-mechanics approach, we present a complete series of atomic force microscopy images of the NaCl(001) surface. For a given atomic structure of a diamond probe-tip [111] oriented, we analyze the results obtained from the two usual imaging modes either based on the monitoring of lateral or vertical forces. By accounting for the atomic relaxation of the whole system for any tip-sample configuration, we were able to get new insights about the achievement of atomic resolution on such substrates. Depending on the tip-sample distance range, the scanning of the NaCl(001) surface results in completely different behaviors associated with these two imaging modes. At very short distance we observed an increase of the apparent corrugation when working with the lateral force mode. The perturbations generated in the images by the presence of localized defects (vacancy and monoatomic step) are also analyzed within this model. These last calculations clearly indicate the fundamental role p...

Optical Near Field Detection and Local Spectroscopy of a Surface: A Self-Consistent Theoretical Study

Optical microscopy by near field detection belongs to the new born family of local probes. This promising technique theoretically allows to image structures with typical sizes smaller than the radiation wavelength (C. Girard and D. Courjon, Phys. Rev. B42, (1990) 9340). The present work generalizes this concept to the local optical spectroscopy of surfaces. Starting from a Lippmann- Schwinger self-consistent equation, we study the near field behavior near a monolayer of metallic nanoparticles deposited on a transparent sample. In this context, we discuss the influence of different external parameters (approach distance, probe size,…) on the spectral resolution.

Fabrication and Electric Conductance of a Finite Atomic Gold Wire: A Theoretical Study

The possibility of making an atomic wire by pushing with an AFM tip some gold atoms adsorbed onto a NaCl(100) surface is discussed. Constant force images of the NaCl(100) surface, of a single gold atom and of a chain of gold atoms adsorbed onto the NaCl(100) surface are presented. A method of pushing a gold atom with the apex of an AFM tip is proposed. The conductance of a gold atomic wire is calculated using the Elastic ScatteringQuantum Chemistry (ESQC) technique.

Self-consistent study of the electromagnetic coupling between a thin probe tip and a surface: implication for atomic-force and near-field microscopy

Abstract A self-consistent formalism based on the use of response functions is developed in order to describe the dispersion equation governing the electromagnetic coupling between a dielectric tip of arbitrary shape and a rough surface. An advantage of such a calculation lies in the possibility of simulating dielectric tips without introducing boundary conditions at the surface of the detector. Connecting with atomic-force microscopy (AFM) and near-field detection with nanometer-size probe will be discussed in this context.

Photon emission rates in photonic band-gap materials

A photonic crystal efficiently controls the radiation rate of an embedded dipolar emitter. The influence of the periodic refractive index patterning on the emitter characteristics is assessed and the efficiency of a dipolar photonic source is calculated for a realistic, three-dimensional photonic crystal. Taking as a starting point the photonic band structure, it is shown that the emission rate is strongly correlated with the density of modes. For an infinite crystal, the computation of the field propagator confirms, in particular, that the emission rate falls to zero in the frequency range defined by the photonic band gap. We specifically consider a photonic crystal with a woodpile structure, offering a wide gap, with a monochromatic oscillating dipole at specific points (in or outside the rods) and orientations in the structure, and compute the emitted fields, expanded in terms of the photonic crystal eigenmodes. Radiation rate enhancements or inhibitions are predicted, according to the frequency and to the direction of the emission.

Moving an Adsorbate with the Tip Apex of a Scanning Probe Microscope: A Comparative Study of the Xe-Cu(110) and Au-NaCl(100) Systems

Some pioneering work has shown that the manipulation of atoms with the tip apex of a scanning probe microscope is a promising new tool for the fabrication of nanoscale structures. So, we have chosen to describe theoretically different manipulation processes for two systems of experimental interest. In a first step, we present a theoretical study of the stability of a Xe atom confined between a STM tip and the (110) face of a fcc metallic substrate. The interaction between the xenon atom and the substrate is calculated by considering Born-Mayer repulsive and van der Waals attractive potentials. In a second part, we investigate the possibility of moving with the tip of an AFM a gold atom weakly chemisorbed on the (100) face of NaCl. In both cases the stability of the adatom under the tip apex is discussed as a function of the tip-substrate distance and different sequences of potential sections are given as the tip is moved above the substrate.

The Eigler Xe Switch: Its Atomic Structure from Xe Energy Minimization and STM Image Calculations

From the calculation of the Xe potential energy on the Cu(110) surface, on a copper tip apex and of the constant current images of this Xe on Cu(110), atomic structures of the tip apex in the “off” and “on” state (during a scan) and of the “tip apex Xe surface” tunnel junction (before scanning) are proposed.