E. V. Alieva

Quick Oxidation of Porous Silicon in Presence of Pyridine Vapor

The oxidation of porous silicon (PS) is an important issue to be considered for a better understanding of the physical and chemical properties of this material in view of its possible application in several technological fields (optoelectronics, optical filters, environmental monitoring, etc.). In this work the quick oxidation of mesoporous PS induced by pyridine vapor in air has been studied by infrared spectroscopy. The logarithmic dependences of the oxidation degree, representing the fraction of Si converted into silicon oxide, on the exposure time to pyridine vapor have been measured. Values of this quantity up to 0.9, depending on the PS porosity and on the exposure time, have been obtained. It has been found that the oxidation continues, although at lower rate, even when pyridine treatment is finished. The possible role of pyridine in this chemical oxidation treatment is suggested.

Sum frequency generation spectroscopy of thin organic films on silver using visible surface plasmon generation

Abstract We present vibrational spectra of thin films of copper phthalocyanine and hexamethylenetetramine on silver obtained by a visible–infrared sum frequency generation (SFG). Excitation of a surface plasmon on the silver layer was used to enhance the efficiency of the SFG process. The free electron laser FELIX was used as a source of a broadband infrared and a pulsed Nd:YLF laser as a source of a visible radiation.

Giant enhancement of sum-frequency generation upon excitation of a surface plasmon-polariton

The generation of the sum frequency of visible (0.5235 μm) and IR (10 μm) radiation on smooth and corrugated silver surfaces is investigated. The sum-frequency signal obtained with a visible-range surface plasmon-polariton excited on a corrugated silver-air interface is found to be more than four orders of magnitude stronger than the signal from a smooth silver surface.

Enhancement of adsorbate vibrations due to interaction with microcavity mode in porous silicon superlattice

Abstract A porous silicon Fabry–Perot microcavity centred in the infrared region was used, after exposure to dodecane (C 12 H 26 ) vapour, to study the interaction of the cavity mode with the C–H vibrations of the adsorbed molecules inside pores. This Fabry–Perot microcavity has been realised by controlling the current and the time of a stepwise anodization procedure of a p + -type silicon wafer in an electrochemical cell with a hydrofluoric acid solution. Splitting of the cavity mode dispersion curve (frequency versus wavevector) and enhancement of the infrared absorption of the adsorbate bands have been studied for various concentrations of dodecane.

Spectroscopy of a thin fullerene film on silver using sum frequency generation enhanced by visible surface plasmon–polaritons

Abstract For the first time the visible–infrared sum frequency generation (SFG) spectrum of a few nm thick fullerene film on silver has been measured in the 490–580 cm−1 region. The SFG yield was enhanced by visible surface plasmon–polaritons excited at the fullerene–silver interface. In the SFG spectrum there are bands present in the infrared and Raman spectra too. In addition one more band near 510 cm−1 was found. We suggest that this band corresponds to a surface specific vibration that appears due to interaction with silver. SFG spectroscopy supporting by the visible surface plasmon–polariton is an excellent tool to study interfacial layers.

Phase measurements of surface electromagnetic waves on silver with excitation through the substrate

Surface electromagnetic waves are excited in the visible and near-IR regions of the spectrum, and interference measurements are performed. Their excitation is effected by a helium-neon laser (3.39, 1.15, and 0.63 µm) on the interface between air and a silver film of thickness 100 µm deposited on a substrate in the form of a prism of fused quartz. The exciting radiation is supplied from the substrate side in a regime of total internal reflection in the prism on the edge of the silver film. The wave vector of the surface electromagnetic wave investigated is determined from the results of phase measurements. The dependence of the efficiency of the excitation of surface electromagnetic waves on the angle of incidence of the exciting radiation onto the substrate is investigated. The real part of the dielectric function of the silver film is calculated.

Manifestation of quantum size effects in optics of ultrathin niobium films

The optical properties of ultrathin (∼nm) niobium films enriched with oxygen are studied by the methods of phase spectroscopy of surface electromagnetic waves (in the far-IR spectral region), IR absorption (in the mid-IR spectral region), and ellipsometry (in the visible spectral region). The films were deposited onto crystal calcium fluoride substrates by the method of high-frequency cathode sputtering. The complex permittivity of the films is calculated from the experimental data. The dependences of both the imaginary and real parts of the permittivity on the film thickness exhibit oscillations with a period of 9 Å, the real part sign being changed during oscillations.

USE OF A MICROCAVITY MODE IN POROUS SILICON SUPERLATTICE TO ENHANCE BAND INTENSITIES IN VIBRATIONAL SPECTRA

We have used a Fabry-Perot type microcavity in porous silicon layered structures to enhance vibrational band intensities in infrared (IR) and Raman spectra. Parameters of the layers in the structure were chosen to have the cavity mode in the spectral region of adsorbate vibrational bands for the IR measurements and near a visible laser wavelength in the Raman experiment. In the IR spectra the enhancement achieved more than one order of magnitude due to photon confinement in the microcavity acting like a multipass cell. In the Raman experiment the enhancement factor of the band intensity was larger than 30. The obtained enhancement was due to the coupling of both laser radiation and Stokes photons of porous silicon with the cavity mode at optimal laser beam incidence and scattering angles.

SUM-FREQUENCY GENERATION SPECTRA OF THIN ORGANIC FILMS ON SILVER ENHANCED DUE TO SURFACE PLASMON EXCITATION

(a) Institute of Spectroscopy, Russian Academy of Sciences, 142092 Troitsk,Moscow region, Russia(b) FOM-Institute for Plasma Physics, P.O. Box 1207, NL-3430 BE Nieuwegein,The Netherlands(c) Istituto di Metodologie Avanzate Inorganiche, CNR, C.P. 10, I-00016 Monterotondo Sc.,Italy(Received May 8, 1999)We have studied vibrational spectra of thin films of copper phthalocyanine and fullerene of differ-ent thicknesses on silver obtained by a visible-infrared sum-frequency generation (SFG). The freeelectron laser FELIX was used as a source of broadband infrared and the pulsed Nd:YLF lasersystem as a source of visible radiation. Excitation of a surface plasmon on silver has allowed toenhance the efficiency of the SFG process. The SFG signal has appeared to be almost independentof the film thickness demonstrating the exclusive contribution of the interfacial layer to the SFGsignal.

Study of crystals in medium-and long-wavelength IR ranges by surface-electromagnetic-wave spectroscopy

First observation of excitation of surface electromagnetic waves (SEW) is reported in the reststrahlen region in for biaxial crystal KTiOPO4 (KTP) using a tunable CO2 laser around 10 µm, and for CaF2, BaF2, MgO (cubic crystals), and LiNbO3 (uniaxial crystal) in the far IR using ith a free-electron laser. The parameters of SEW propagation in these crystals have been obtained by the interference method of SEW phase spectroscopy, and the possibility of determining the complex dielectric permittivity of crystals from the SEW propagation parameters demonstrated in the range of SEW existence.