E. Haro-Poniatowski

Growth of LiMn2O4 thin films by pulsed-laser deposition and their electrochemical properties in lithium microbatteries

Films of LiMn2O4 were grown by pulsed-laser deposition (PLD) onto silicon wafers using sintered targets which consisted in the mixture of LiMn2O4 and Li2O powders. The film formation has been studied as a function of the preparation conditions, i.e. composition of the target, substrate temperature, and oxygen partial pressure in the deposition chamber. Composition, morphology and structural properties of PLD films have been investigated using Rutherford backscattering spectrocopy, scanning electron microscopy, X-ray diffraction and Raman scattering spectroscopy. The films deposited from target LiMn2O4+15% Li2O have an excellent crystallinity when deposited onto silicon substrate maintained at 300°C in an oxygen partial pressure of 100 mTorr. It is found that such a film crystallizes in the spinel structure (Fd3m symmetry) as evidenced by X-ray diffraction. Well-textured polycrystalline films exhibit crystallite size of 300 nm. Pulsed-laser deposited LiMn2O4 thin films obtained with a polycrystalline morphology were successfully used as cathode materials in lithium microbatteries. The Li//LiMn2O4 thin film cells have been tested by cyclic voltammetry and galvanostatic charge-discharge techniques in the potential range 3.0–4.2 V. Specific capacity as high as 120 mC/cm2 μm was measured on polycrystalline films. The chemical diffusion coefficients for the LixMn2O4 thin films appear to be in the range of 10−11–10−12 cm2/s. Electrochemical measurements show a good cycleability of PLD films when cells are charged-discharged at current densities of 5–25 μA/cm2.

Structural characterization of TiO2 thin films obtained by pulsed laser deposition

The structural characterization by Raman spectroscopy and X-ray diffraction of TiO2 thin films obtained by pulsed laser deposition is reported. The substrate temperature and the oxygen pressure effects are investigated. The main result is that rutile TiO2 thin films are obtained at low substrate temperatures. The film growth occurred mainly in the (110) direction.

Growth of V2O5 thin films by pulsed laser deposition and their applications in lithium microbatteries

Abstract Vanadium pentoxide thin films were obtained by pulsed-laser deposition onto various substrates. The growth was performed at different oxygen pressures and substrate temperatures. It is found that the films deposited on glass are amorphous and exhibit a polycrystalline structure upon thermal treatment as evidenced by X-ray diffraction and Raman scattering spectroscopy. The films deposited onto silicon wafer have an excellent crystallinity when deposited at substrate temperatures of 300°C and an oxygen pressure of 50 mTorr. V2O5 thin films obtained by this method were successfully used as a cathode materials in lithium microbatteries. Electrochemical measurements show a good cyclability of pulsed laser deposited films.

Micro-Raman characterization of WO3 and MoO3 thin films obtained by pulsed laser irradiation

Abstract Thin films of MoO3 and WO3 have been obtained by pulsed laser deposition. The structure of the films and of the splashed species were studied by Raman microscopy. In the case of WO3 a single monoclinic phase was observed. For MoO3 the deposited material corresponds to its metastable phase known as β-MoO3. In the splashed species a mixture of the α-MoO3 and β-MoO3 phases is found.

Structural study of lithium titanium mixed oxides prepared by sol-gel process

A structural study, using TGA-DSC analysis, X-ray diffraction, Raman scattering and FT Infrared absorption, is performed on mixed titanium lithium oxide with 20% of lithium prepared by sol-gel process. The structure is investigated as a function of the annealing temperature. At low temperatures the sample is in the anatase phase and transforms to the rutile phase near 500°C. The crystallite size of rutile TiO2 increases from 40 to 100 nm as the temperature increases. However the size increase presents some discontinuity at temperature around 600°C. At thermal treatment temperatures from 500°C to 850°C the presence of LiTi2O4 in the sample is clearly observed. Finally at 1000°C the sample is composed by a mixture of rutile TiO2 and Li2Ti3O7.

Effect of thickness on the photoluminescence of silicon quantum dots embedded in silicon nitride films

In this work, the effect of film thickness on the photoluminescence (PL) spectra of Si quantum dots embedded in silicon nitride films is investigated experimentally and theoretically. The films were deposited by remote plasma enhanced chemical vapor deposition using the same SiH2Cl2/H2/Ar/NH3 mixture and deposition conditions, in order to obtain films with similar composition and approximately equal average size (∼3.1 nm) of Si quantum dots. Only the deposition times were varied to prepare five samples with different thicknesses ranging from ∼30 nm to 4500 nm. Chemical characterization by Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy were carried out in order to check that the composition in all films was the same. The structure, average size, and size distribution of the Si quantum dots were deduced from High-Resolution Transmission Electron Microscopy. The thickness of the films was determined by ellipsometry and interferometry of UV-Vis transmission spectra. It was found ...

Plasma dynamics inferred from optical emission spectra, during diamond-like thin film pulsed laser deposition

Abstract Diamond-like thin films were produced via PLD with the fundamental line of a Nd:YAG laser, while the plasma dynamics were studied non-destructively by emission spectroscopy. Spectra obtained by analysing the plasma optical emission at various distances from the ablated graphite surface show how the composition and temperature vary within the plasma plume. The collected data allow the identification of various emitting species at different regions of the expanding plasma and estimation of their velocities. The further ahead in the plume, the more the ablated material is ionised. Temperatures are determined from the continuous broad background, while the plasma cools as it expands. The influence of substrate temperature on the resulting film structure is also studied through Raman scattering measurements. Optical microscope pictures are taken to evaluate surface quality. Plasma ionisation degree and kinetic energies are enough to grow diamond-like films, but high substrate temperatures favour graphitic order.

Structure and electrochemistry of thin-film oxides grown by laser-pulsed deposition

Thin films of V2O5, LiCoO2 and LiMn2O4 were grown by pulsed-laser deposition in the view of their use in lithium microbatteries. Lithiated polycrystalline crystalline thin dense films grown without post-deposition annealing were formed onto substrates maintained at low temperature (300 °C) from a sintered composite target including Li2O as additive. The structural characterizations of these films have been carried out by X-ray diffraction and Raman scattering spectroscopy. The electrochemical features of thin films are investigated by cyclic voltammetry and their charge-discharge profiles in lithium microbatteries are shown.

Potential of bismuth nanoparticles embedded in a glass matrix for spectral-selective thermo-optical devices

The optical transmission at a fixed visible wavelength of Bi nanoparticles embedded in a dielectric is known to show a sharp hysteretic evolution as a function of the temperature due to the reversible melting-solidification of the nanoparticles. In this work, we explore the temperature-dependent optical response of Bi nanoparticles embedded in a doped germanate glass (GeO2-Al2O3-Na2O) in a broad range from the visible to the near infrared. The transmission contrast induced by melting of the nanoparticles is shown to be strongly wavelength-dependent and evolves from positive to negative as the wavelength increases. This behaviour is well modelled using effective medium calculations, assuming that the nanoparticles size, shape, and distribution are unmodified upon melting, while their dielectric function turns from that of solid Bi to that of liquid Bi thus modifying markedly their optical response. These results open a route to the spectral tailoring of the thermo-optical response of Bi nanoparticles-based...

Spectroscopic studies of two perpendicularly interacting carbon plasmas generated by laser ablation

The interaction of two plasmas generated by laser ablation from two perpendicular carbon (graphite, 99.99% purity) targets was analyzed by optical emission spectroscopy. The 1064 nm line of a Nd:YAG laser was used as energy source. Spatial and temporal measurements were performed. The covered spectral range was from 280 to 740 nm. Time of flight measurements were performed to determine the kinetic energies of different excited species. It was found that the excited species were more energetic; however, their lifetimes were shorter when the two plasmas were interacting. Carbon thin films were deposited at different positions relative to the plasmas and subsequently characterized by scanning electron microscopy and Raman spectroscopy.