Sergei Kostcheev

Short Range Plasmon Resonators Probed by Photoemission Electron Microscopy

Short range surface plasmon resonators are investigated at the nanometer scale. Gold nanorods (30 nm in diameter) were microfabricated and probed by photoemission electron microscopy under direct laser light excitation. Resonances presenting various numbers of lobes occur for specific rod lengths. A simple analytical model shows that the successive resonant lengths differ by a multiple of one-half of the wavelength of the supported short-range surface plasmon polariton.

Tuning of an Optical Dimer Nanoantenna by Electrically Controlling Its Load Impedance

Optical antennas are elementary units used to direct optical radiation to the nanoscale. Here we demonstrate an active control over individual antenna performances by an external electrical trigger. We find that by an in-plane command of an anisotropic load medium, the electromagnetic interaction between individual elements constituting an optical antenna can be controlled, resulting in a strong polarization and tuning response. An active command of the antenna is a prerequisite for directing light wave through the utilization of such a device.

Optimization of SERS-active substrates for near-field Raman spectroscopy

As a first step towards near-field Raman, we chose to study surface enhanced Raman scattering (SERS)-active substrates to cope with the weakness of Raman scattering (small cross-section and low concentration). We concentrated our work on localized surface plasmon (LSP) since they turned out to play a great part in SERS and we put forward the relation between LSP resonance and Raman enhancement. Roughness of our samples is controlled either by annealing process or electron-beam lithography (EBL); this latter technique proved to best suit to our study. Substrates are characterized by extinction spectroscopy which determines the LSP resonance and then Raman spectrum of a probe molecule, trans-1,2-bis(4-pyridyl)ethylene (BPE) is recorded. We show that maximum of enhancement is obtained when the LSP resonance is red-shifted (50 nm) compared to the excitation laser line (632.8 nm).

Optical properties of metal nanoparticles as probed by photoemission electron microscopy

Interaction of light with metallic nanostructures exhibit resonances specific to eigenmodes of collective electron motion known as plasmon modes. Both these resonances and effects of electromagnetic singularities lead to local field enhancement. Photoemission electron microscopy (PEEM) was recently used to image the electrons photoemitted from these local effects. Here we report on a full PEEM spectral study of localized surface plasmons excited on nanoparticles. In particular, we show strong spectral similarities between the PEEM signal and optical extinction as a function of the incident wavelength, establishing the photoemission microscopy as a valuable tool for investigating the optical properties of metal nanoparticles.

Characterizations of Ohmic and Schottky-behaving contacts of a single ZnO nanowire

Current-voltage and Kelvin probe force microscopy (KPFM) measurements were performed on single ZnO nanowires. Measurements are shown to be strongly correlated with the contact behavior, either Ohmic or diode-like. The ZnO nanowires were obtained by metallo-organic chemical vapor deposition (MOCVD) and contacted using electronic-beam lithography. Depending on the contact geometry, good quality Ohmic contacts (linear I-V behavior) or non-linear (diode-like) contacts were obtained. Current-voltage and KPFM measurements on both types of contacted ZnO nanowires were performed in order to investigate their behavior. A clear correlation could be established between the I-V curve, the electrical potential profile along the device and the nanowire geometry. Some arguments supporting this behavior are given based on technological issues and on depletion region extension. This work will help to better understand the electrical behavior of Ohmic contacts on single ZnO nanowires, for future applications in nanoscale field-effect transistors and nano-photodetectors.

External control of the scattering properties of a single optical nanoantenna

We present a mechanism to control the scattering properties of individual optical nanoantennas by applying an external electric field. We find that by electrically tuning an anisotropic load medium the scattered intensity becomes voltage-dependent. We also demonstrate that the scattering diagram of the antenna can be externally adjusted. This on-demand command opens up the possibility to tune an antenna without changing its geometrical parameters.

Nanofabrication for Plasmonics

Within the last 15 years, the scientific interest for individual or assembly of metallic nanostructures of well-defined size, geometry, and distribution has constantly increased. This paper aims at giving a comprehensive overview of the different nanofabrication techniques used in plasmonics including focused electron- and ion-beam lithography as well as the major associated challenges and issues. Alternative techniques, such as interference lithography and self-assembly techniques, are also discussed apart from material-related issues. The paper is divided into four parts emphasizing on metallic structures fabrication on planar surface, metallic structures fabrication on nonplanar surfaces, metallic structure surface functionalization and hybrid nanostructures fabrication. Finally, alternative techniques and forthcoming issues, such as material quality, nanostructuring on large scale, and plasmonic integration, are also addressed.

On- and off-axis second harmonic generation from an array of gold metallic nanocylinders

The optical second harmonic (SH) response from gold metallic nanocylinders with diameters of 80 and 120 nm arranged in hexagonal arrays has been determined as a function of the input fundamental polarization angle for the on- and off-axis transmission geometries and crossed output polarization configurations. For the on-axis transmission geometry, the nonlinear response of the nanocylinders is shown to be mainly incoherent, of pure electric dipole nature and arising from the breaking of the centrosymmetric shape of the body of the cylinders in a plane parallel to the substrate surface. Small angle off-axis experiments however show that the coherent contribution to the nonlinear response is size dependent suggesting that, besides the out-of-plane nonlinearity, retardation effects may also play a nonnegligible role.

Enhanced Raman scattering of ZnO nanocrystals in the vicinity of gold and silver nanostructured surfaces.

nonresonant surface enhanced Raman scattering by optical phonons of ZnO nanocrystals on and beneath silver and gold island films is reported. For both configurations comparable SERS efficiency is observed, proving their potential utility. Variations in peak intensities can be attributed to difference in the morphology of island films on and beneath nanocrystals as well as to variation of the interface between semiconductor and metal. The dominant peaks in the SERS spectra are assigned to surface optical phonon modes.

Enhanced stimulated emission in ZnO thin films using microdisk top-down structuring

Microdisks were fabricated in zinc oxide (ZnO) thin films using a top-down approach combining electron beam lithography and reactive ion etching. These microdisk structured thin films exhibit a stimulated surface emission between 3 and 7 times higher than that from a reference film depending on the excitation power density. Emission peak narrowing, reduction in lasing threshold and blue-shifting of the emission wavelength were observed along with enhancement in the emitted intensity. Results indicate that this enhancement is due to an increase in the internal quantum efficiency combined with an amplification of the stimulated emission. An analysis in terms of waveguiding is presented in order to explain these effects. These results demonstrate that very significant gains in emission can be obtained through conventional microstructuration without the need for more onerous top-down nanostructuration techniques.