National Institute Of Materials Physics - Romania

In this letter, we present a study of surface-enhanced Raman spectra of thin layers of phthalocyanine (Pc) complexes deposited on Ag and Au rough surfaces. The materials of this work are MgPc (monophthalocyanine) and the asymmetrical lutetium bisphthalocyanine (tBu)(4)PcLuPcCl8 (Pc'LuPc ") under three oxidation states. Enhancement of specific bands is observed depending on the surface and the oxidation state. SERS signatures of neutral, oxidised and reduced Pc'LuPc " are identified.

Surface-enhanced Raman scattering (SERS) has proved to be an effective technique for studying the structural properties of conducting polymer thin films. The enhancement process has a twofold origin, electromagnetic and chemical, The electromagnetic enhancement, which is the dominant mechanism in SERS generation, consists in the excitation of localized and delocalized surface plasmons (SPs) in the metallic support of the thin film, The Raman emission of the adsorbed molecules on the metal surface (the most efficient being Ag, Au and Cu) is due to the intense evanescent electromagnetic field located at the interface between the metal and the surrounding medium. The second enhancing mechanism for SERS is of chemical origin, involving the formation of new chemical bonds between the molecules and the metal surface, with the polarizability thus becoming considerably higher than that of the free molecules. This mechanism is as a rule accompanied by a metal-molecule or molecule-metal charge transfer, which partly accounts for the success of the SERS studies on conducting polymers. Unfortunately, these studies have revealed that the chemical effects at the polymer-metal interface varied substantially depending on the various types of polymer and metallic support. In this context, polyaniline containing two different entities (a reduced and an oxidized state) in its repeating units exhibits specific alterations in its SERS spectra depending on the type of metallic support. This paper presents new results concerning the structure of emeraldine-base and emeraldine-salt polyaniline thin films deposited on rough Ag and Au supports. The effect on the SERS spectra of the polymer-metal and polymer-ambient interface chemical reactions is also described. The presence of an interface compound depending on the oxidizing properties of the metallic support has a strong influence on the SERS spectra, no matter how the PAN films were deposited on the support (whether by solvent evaporation or by an electrochemical process, i.e. cyclic voltammetry). When an emeraldine base is doped with HSO4- ions, it turns into an emeraldine salt, which exhibits a disordered state in its macromolecular chain, leading to a modified profile of the similar to 1162 cm(-1) Raman line which is associated with the C-H bond of the quinoid ring. The Lorentzian profile is altered by the addition of a Gaussian profile component. For a rough Ag support, the SERS spectra show that the transformation of emeraldine base films into emeraldine salt films is a reversible process, Copyright (C) 1999 John Wiley & Sons, Ltd.

The effect of tin impurities on optical spectra of thermally deposited AsSe films doped with Sn (1 to 10 at%) was studied in a wide energy interval from 0.8 to 6.2 eV by combination of reflection, absorption, photoresponse and photocapacitance spectroscopies. Most changes have been detected at the fundamental absorption edge over which a correlation between the band tail width and optical gap is demonstrated for various tin concentrations. The tin induced absorption band associated with a localized energy level at about 1.6 eV in the gap was revealed. Distinct variations in the reflectivity spectra of the fundamental absorption region suggest a tin assistance in the formation of the valence band states of the material.

Cyclic voltammetry and impedance spectroscopy were used for study of polyaniline in acid solutions. Impedance spectra were presented both as Bode diagrams and Nyquist representations. The capacitive charging behaviour and anion (ClO4-, HSO4-) insertion/elimination reaction of the polymer film were discussed on the basis of a simplified Randles circuit model. The examined scanning electron micrographs have also shown that the nature of dopant anion changes the film morphology.

After being dispersed in liquid solvents (Ethanol, CHCl3), conducting polymers and singlewalled nanotubes have been deposited on ruguous substrats (Au, Ag, Cu). With FT Raman technique (laser excitation : 1064 nm), we have obtained SERS signal of both conductiong polymers and singlewalled nanotubes. The Raman signals change with substrat and/or solvent, which could be correlated with the size of clusters formed at the surface and then to the deposition mechanism. The main advantage of the >SERS technique will be emphasized in terms of enhancement as a powerful technique to study nanoparticles.

TiN/Si structures were deposited on Si wafers by pulsed laser deposition technique. The highly conductive TiN films were grown on heated (100) Si substrates by laser ablation of a high purity Ti target in nitrogen reactive atmosphere. Subsequently, the Si layer was deposited by laser ablation of a Si target in vacuum (down to 10(-6) mbar) or in low pressure inert gas. The nitrogen gas pressure and the substrate temperature were found to strongly influence the TiN film structure and orientation. The degree of crystallinity of the Si layer grown on the TiN film was found to depend on Si/TiN collector temperature. Values below 550 degrees C (the threshold of TiN oxidation activation) were used in the experiments. Techniques as X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), High Resolution Transmission Electron Microscopy (HRTEM), Scanning Force Microscopy (SFM) have been used to characterize the deposited structures. The TiN/Si structure rectifying properties were tested. The obtained Si/TiN/Si structure could be suitable for the building of Permeable Base Transistor (PBT, vertical MESFET) devices. (C) 1999 Elsevier Science S.A. All rights reserved.

Multilayer Pb(ZrTi)O-3 (PZT)/TiN/Si structures were grown by two subsequent laser ablation processes in reactive atmosphere. First, a fee-oriented TiN film was deposited by laser ablation of a Ti target in high-purity nitrogen reactive gas. Subsequently, a crystalline, piezoelectric PZT film was grown by reactive ablation of a PZT target in oxygen atmosphere. Both deposition processes were conducted at quite low Si(100) substrate temperature: 350 degrees C for TiN and 370 degrees C for PZT, in the same experimental setup (Nd-YAG laser, lambda = 1060 nm, energy/pulse 0.3 J, t(FWHM) = 10 ns). TiN film properties were analyzed by XRD and electric measurements. After the deposition of the PZT layer, the obtained structure was first characterized by XRD, SEM and SIMS techniques. Testing measurements performed after the deposition by thermal evaporation of an Al layer as top electrode on the PZT/TiN/Si structure confirm that they can be used as sensor transducer element. The TiN (as high conductive nitride) layer replaces the former Au layer used as bottom electrode. In this way, the Au diffusion inside the Si substrate, as well as in the deposited layer, is avoided, as could be observed from a comparative study of the SIMS spectra recorded for PZT/TiN/Si and PZT/Au/Si configurations. (C) 1999 Elsevier Science S.A. All rights reserved.

In this paper, we present Surface Enhanced Raman Scattering (SERS) experiments performed successfully on some conducting polymers and carbon nanotubes deposited in thin films on rough metallic surfaces. The enhancement mechanism in SERS has a twofold origin: electromagnetic and chemical. The electromagnetic enhancement is, however, the dominant mechanism and consists in the excitation of localized and delocalized surface plasmons (SP). The second enhancing mechanism for SERS, not yet convincingly supported by experimental data, is of chemical origin. This mechanism is due to the increase of the polarizability of the molecules on the metal surface under the action of the incident radiation, leading to the formation of new chemical bonds between the molecules and the metal surface. Unfortunately, the experimental data available to argue the presence of a chemical process are scarce and scattered. In this paper, we try to present some details regarding this aspect. In order to do so, we studied poly 3-hexylthiophene (3-PHT) and polyaniline (PAN) as a function of the type of the rough metallic support (Ag, Au or Cu), the oxidization state and thickness of the polymer layer. We studied also carbon single walled nanotubes. Our experiments reveal the existence of a chemical surface effect. The results obtained for 3-PHT show that SERS spectra depend on the oxidizing properties of the metal surface and on the nature of the solvent. This dependence is explained by the existence of some interfacial reactions that lead to the formation of interface compounds. The SERS measurements reported here reveal an increase of the intensities of the Raman lines, accompanied by a modification of the corresponding intensity ratios, when the degree of doping is increased. We observe for the first time by SERS spectroscopy that doping of 3-PHT with FeCl3 leads to the appearance of a state of disorder in the structure of the macromolecular chain, as a result of steric hindrance effects. The type of the rough metallic support can modify SERS spectra and such an effect is clearly shown for the polyaniline case. No such dependence on metallic support type is observed on the SERS spectra of carbon nanotubes. (C) 1999 Published by Elsevier Science S.A. All rights reserved.

The photo-structural transformations induced by ultraviolet (UV) radiation in Ge27Sb13Se60 amorphous thin films prepared by thermal evaporation method have been investigated. The mechanical, optical and structural data were investigated before and after irradiation of the fresh and annealed films. The modifications of the film structure and properties depend essentially on the state of the films: fresh or annealed below glass transition temperature.

Metal structures in quartz crystals were obtained by electrodiffusion in air with different metal sources at the anode. The dynamics and the properties of these structures, for different conditions of temperature, applied electric field and anode material were studied. Current-voltage characteristics, Arrhenius plot, optical microscopy, electronic microscopy and thermoluminescence glow curve were employed. (C) 1999 Elsevier Science B.V. All rights reserved.