Properties of silicon dioxide layers with embedded metal nanocrystals produced by oxidation of Si:Me mixture

A two-dimensional layers of metal (Me) nanocrystals embedded in SiO2 were produced by pulsed laser deposition of uniformly mixed Si:Me film followed by its furnace oxidation and rapid thermal annealing. The kinetics of the film oxidation and the structural properties of the prepared samples were investigated by Rutherford backscattering spectrometry, and transmission electron microscopy, respectively. The electrical properties of the selected SiO2:Me nanocomposite films were evaluated by measuring C-V and I-V characteristics on a metal-oxide-semiconductor stack. It is found that Me segregation induced by Si:Me mixture oxidation results in the formation of a high density of Me and silicide nanocrystals in thin film SiO2 matrix. Strong evidence of oxidation temperature as well as impurity type effect on the charge storage in crystalline Me-nanodot layer is demonstrated by the hysteresis behavior of the high-frequency C-V curves

Raman Spectroscopy of V4O7 Films

A thin film of vanadium oxide Magnéli phase V4O7 was produced using cathodic arc sputtering. X-ray diffraction, Rutherford backscattering spectrometry and Raman investigations confirmed the formation of this phase. The Raman spectrum of V4O7 differs considerably from the spectrum of another Magnéli oxide, V3O5, showing that Raman spectroscopy is an excellent tool for distinguishing between these two phases. Temperature-dependent Raman measurements revealed a significant change of the spectra near the V4O7 metal–insulator phase transition

Raman Spectroscopy of V4_4O7_7 Films

A thin film of vanadium oxide Magnéli phase V$_4$O$_7$ was produced using cathodic arc sputtering. X-ray diffraction, Rutherford backscattering spectrometry and Raman investigations confirmed the formation of this phase. The Raman spectrum of V$_4$O$_7$ differs considerably from the spectrum of another Magnéli oxide, V$_3$O$_5$, showing that Raman spectroscopy is an excellent tool for distinguishing between these two phases. Temperature-dependent Raman measurements revealed a significant change of the spectra near the V$_4$O$_7$ metal–insulator phase transition

Correlation between Raman spectra and oxygen content in amorphous vanadium oxides

Amorphous vanadium oxide films were produced using a cathodic arc deposition technique. Varying oxygen pressure in a chamber during the film growth, we obtained the samples with different oxygen concentration. Elemental composition of our films was studied by Rutherford backscattering spectroscopy and energy dispersive X-ray analysis. Raman characterization of the samples showed the strong influence of oxide stoichiometry on the spectra: the main feature was attributed to stretching vibrations of vanadyl bonds and its position shifted from 879 to 937 cm$^{−1}$ upon changing the V/O ratio from VO$_2$ to V$_2$O$_5$. An explanation of such behavior and an empirical formula of this dependence were suggested

Effect of PLD growth conditions on the structural and ferroelectric properties of perovskite thin films

Ultrathin ferroelectric (FE) films have recently got much attention in the context of the non-volatile memory devices. Over the last decade, the rapidly improving expertise in the fabrication of the structurally perfect complex oxide FE layers have led to the fabrication of heterostructures with intriguing physical and functional properties. In particular, ultrathin heteroepitaxial BaTiO3 (BTO) films have been utilized as a storage medium in the FE tunnel junctions [1], and exhibited giant bulk photovoltaic effect [2]. Pulsed Laser Deposition (PLD) has recently emerged as an excellent tool to grow epitaxial oxide heterostructures, particularly comprising ultrathin FE BTO and SrTiO3 (STO) layers. In this work, we report on the effect of PLD growth conditions of BTO and STO on MgO and Si substrates on their structural and FE properties. We show that the structural properties of the oxide layer strongly depends on a precise control over the partial O2 pressure in the growth chamber, substrate temperature and laser ablation parameters. The structure of 3-100 nm PLD grown layers was monitored in situ by RHEED, and further analyzed ex situ by XRD, XRR, AFM and TEM. The ferroelectric properties were investigated by piezoresponse force microscopy. BTO and STO thin films grown at the optimized conditions are monodomain ferroelectrics with the polarization direction perpendicular to the substrate. 1. A. Zenkevich et al. APL 102 062907 (2013). 2. A. Zenkevich et al. PRB 90 161409 (2014

Properties of silicon dioxide layers with embedded metal nanocrystals produced by oxidation of Si:Me mixture

Abstract A two-dimensional layers of metal (Me) nanocrystals embedded in SiO2 were produced by pulsed laser deposition of uniformly mixed Si:Me film followed by its furnace oxidation and rapid thermal annealing. The kinetics of the film oxidation and the structural properties of the prepared samples were investigated by Rutherford backscattering spectrometry, and transmission electron microscopy, respectively. The electrical properties of the selected SiO2:Me nanocomposite films were evaluated by measuring C-V and I-V characteristics on a metal-oxide-semiconductor stack. It is found that Me segregation induced by Si:Me mixture oxidation results in the formation of a high density of Me and silicide nanocrystals in thin film SiO2 matrix. Strong evidence of oxidation temperature as well as impurity type effect on the charge storage in crystalline Me-nanodot layer is demonstrated by the hysteresis behavior of the high-frequency C-V curves.</p

Performance and Mechanism of Photoelectrocatalytic Activity of MoSx/WO3 Heterostructures Obtained by Reactive Pulsed Laser Deposition for Water Splitting

This work studies the factors that affect the efficiency of the photoelectrochemical hydrogen evolution reaction (HER) using MoSx/WO3 nano-heterostructures obtained by reactive pulsed laser deposition (RPLD) on glass substrates covered with fluorinated tin oxide (FTO). Another focus of the research is the potential of MoSx nanofilms as a precursor for MoOz(S) nanofilms, which enhance the efficiency of the photo-activated oxygen evolution reaction (OER) using the MoOz(S)/WO3/FTO heterostructures. The nanocrystalline WO3 film was created by laser ablation of a W target in dry air at a substrate temperature of 420 &deg;C. Amorphous MoSx nanofilms (2 &le; x &le; 12) were obtained by laser ablation of an Mo target in H2S gas of varied pressure at room temperature of the substrate. Studies of the energy band structures showed that for all MoSx/WO3/FTO samples, photo-activated HER in an acid solution proceeded through the Z-scheme. The highest photoelectrochemical HER efficiency (a photocurrent density ~1 mA/cm2 at a potential of ~0 V under Xe lamp illumination (~100 mW/cm2)) was found for porous MoS4.5 films containing the highest concentration of catalytically active sites attributed to S ligands. During the anodic posttreatment of porous MoSx nanofilms, MoOz(S) films with a narrow energy band gap were formed. The highest OER efficiency (a photocurrent density ~5.3 mA/cm2 at 1.6 V) was detected for MoOz(S)/WO3/FTO photoanodes that were prepared by posttreatment of the MoSx~3.2 precursor. The MoOz(S) film contributed to the effective photogeneration of electron&ndash;hole pairs that was followed by the transport of photoelectrons from MoOz(S) into the WO3 film and the effective participation of holes possessing strong oxidation ability in the OER on the surface of the MoOz(S) film

LASER-INDUCED NANOPARTICLE FORMATION IN LIQUIDS: INVOLVED MECHANISMS AND ROLE OF THE EXPERIMENTAL PARAMETERS

International audienceLaser ablation in liquids is a versatile and promising method for synthesis of colloidal nanoparticles (NPs) that are particularly attractive for bio-sensing, medical application, as well as for catalysis [1]. In the experiments, NPs of different materials are successfully produced by using laser systems with various pulse durations, shape, wavelengths, and fluence. The major mechanisms involved in the formation of these NPs are, however, still under discussionHere, we focus our attention at the better understanding of the physical processes involved in NPs formation by laser ablation in liquids. For this, a series of both experimental and numerical studies are performed. In particular, by using different laser systems with pulse duration from femtosecond to CW range, metallic NPs are obtained with different mean size and size distributions. Furthermore, the role of the solution concentration, liquid properties and of laser-induced fragmentation is demonstrated [1]. To analyze these results, multi-physical numerical modeling is performed. First, laser ablation is modeled for various laser fluences [2,3]. Simulation results show the beginning of the formation of the ablation plume, shock wave, a void/bubble in front of the target. The bubble is formed only above a well-defined both target and liquid-dependent threshold. It then collapses and the target is reheated, so that more NPs originate from this effect. Later, diffusion-driven nucleation and collision growth enter into play. In addition, laser-induced fragmentation and growth of nanoparticles are examined in liquids [4]. The resulted nanoparticles are particularly attractive for bio-sensing, medical application, as well as for catalysis. First, laser energy absorption is considered. The role of laser wavelength is underlined. Then, ultra-short laser-induced fragmentation is considered. The obtained results help us to elucidate the roles of thermal, mechanical and electrostatic effects in the particle decomposition. The absorption cross sections are calculated based on the generalized Mie theory. In addition, combined FDTD-rate equation calculations are carried out revealing a considerable field enhancement around the particle [5]. These results agree with the experiments.Finally, the obtained results demonstrate that the major decomposition mechanism mostly depends on the particle size, laser wavelength and both particle and liquid properties. It is found that as a result of a quite moderate ultra-short laser irradiation, only melting and partial evaporation occurs. With the increase of laser fluence, particle decomposition is observed resulting from both thermal and mechanical effects. The role of thermionic emission [6] and the possibility of Coulomb explosion are also discussed. The results may help in the analysis of the final NP's size distributions.Support from France-Russia collaborative grant PICS 6106 is gratefully acknowledged.[1] K. Maksimova, Synthesis of novel nanomaterials by ultra-short laser ablation in liquids for biomedical applications, PhD thesis, Aix-Marseille University (2014)[2] M.E. Povarnitsyn, T.E. Itina, P.R. Levashov, K.V. Khishchenko, Phys Chem Chem Phys 15(9) 3108-3114, (2013)[3] T. E. Itina, J. Chem. Phys. C 115 (12) 5044-5048 (2010)[4] L. Delfour and T. E. Itina, Proceedings of ALT 2014, Cassis, France (2014)[5]A. Rudenko , JPh. Colombier T. E. Itina, PIERS 2015, (2015