M. Martino

Pulsed laser deposition of active waveguides

We report on the pulsed laser deposition (PLD) of thin films of chalcogenide and tellurite glasses doped with RE ions. The depositions were performed in vacuum, for chalcogenide films, and in a low oxygen pressure for the tellurite films by using an excimer laser. After the deposition, the morphological, structural, optical and spectroscopical characteristics are analysed by different techniques: Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Rutherford Backscattering Spectrometry (RBS), optical profilometry, m-lines spectroscopy, photoluminescence etc. The experimental results demonstrated that PLD is a suitable technique for the realisation of films of complex materials for optoelectronic and photonic applications.

Poly-(3-hexylthiophene)/[6,6]-phenyl-C61-butyric-acid-methyl-ester bilayer deposition by matrix-assisted pulsed laser evaporation for organic photovoltaic applications

A poly-(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM) bilayer structure has been realized by single step matrix-assisted pulsed laser evaporation (ss-MAPLE) technique using the same solvent for both the polymers under vacuum conditions. Our ss-MAPLE procedure allows the fabrication of polymeric multilayer device stacks, which are very difficult to realize with the conventional solvent assisted deposition methods. A proof of concept bilayer P3HT/PCBM solar cell based on ss-MAPLE deposition has been realized and characterized. This demonstration qualifies ss-MAPLE as a general and alternative technique for the implementation of polymeric materials in hetero-structure device technology.

Synthesis of pure titanium nitride layers by multipulse excimer laser irradiation of titanium foils in a nitrogen-containing atmosphere

Experimental results are reported concerning the synthesis of pure, hard, and adherent titanium nitride layers by multipulse excimer (λ=308 nm) laser irradiation in a nitrogen or ammonia atmosphere. It is shown that the process is more efficient when the irradiation is performed in a nitrogen atmosphere. The general characteristics of synthesized surface compound layers are compatible with the requirements of utilization in microelectronics.

Laser-reactive ablation deposition of silicon-nitride films

Silicon-nitride films were deposited on silicon waters by XeCl (308 nm) excimer-laser ablation of silicon in low-pressure (0.05–5 mbar) ammonia atmospheres. Series of 10 000 pulses at the repetition rate of 8 Hz were directed to the target surface. The fluence was set at about 5 J/cm2. Pulse duration was about 30 ns. The deposited films were characterized by different techniques (X-ray diffraction, X-ray photoelectron spectroscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry, scanning electron microscopy, profilometry). Silicon-nitride films with thickness close to 1 μm were obtained under specific experimental conditions.

Oxidation interference in direct laser nitridation of titanium: relative merits of various ambient gases

Abstract A comparison is performed between the relative merits of using an ambient NH 3 atmosphere or a stoichiometrically equivalent N 2 -H 2 (1:3) mixture for the direct laser nitridation of titanium samples by multipulse excimer laser ( λ = 308nm) irradiation. It is shown that the N 2 -H 2 mixture proves more effecient in inhabiting the unwanted interference of the oxidation process and that the whole process proceeds through the action of an erosion plasma on a molten layer covering the laser-irradiated area.

Study of CN binding states in carbon nitride films deposited by reactive XeCl laser ablation

Carbon nitride films, deposited on 〈111〉 Si substrates at room temperature by XeCl laser ablation of graphite targets in low pressure (1, 5, 10 and 50 Pa) N2 atmosphere at the fluence of 16 J/cm2 (∼0.5 GW/cm2) have been submitted to accurate X-ray photoelectron spectroscopy (XPS) investigations in order to study the CN chemical bonding in the films. Multiple binding energy values have been obtained. The N 1s peak of the XPS spectra indicates three different binding states of nitrogen atoms to C atoms, while the C 1s peak, apart from the binding states to nitrogen atoms, indicates other bonding states with regard to carbon atoms.

Excimer laser reactive ablation: An efficient approach for the deposition of high quality TiN films

The successful deposition of TiN films on Si wafers by excimer (λ=308 nm) multipulse laser ablation of Ti in a low pressure N2 jet is reported in this article. The films are particularly pure, entirely consisting of polycrystalline fcc TiN. One difficulty still seems to be related to the presence of small droplets probably ejected in a liquid phase. According to the analyses, TiN is formed on Ti target with small contributions only, if any, of the next transit through gas and final deposition onto the Si wafer support.

Synthesis and deposition of silicon nitride films by laser reactive ablation of silicon in low pressure ammonia: A parametric study

The UV laser (λ=308 nm) ablation of silicon wafers in 1 mbar ambient ammonia results in the deposition of pure and uniform film of amorphous silicon nitride. At low pressures of NH3 (of several to several tens of μbar), the deposited films are a mixture of amorphous silicon nitride, amorphous nonstoichiometric silicon nitride, and amorphous silicon. The contamination with oxygen is low and is more evident at lower pressures. At ammonia pressures 0.1–1 mbar, the films also contain a certain fraction of hydrogen. Droplets of polycrystalline Si cover the surfaces of some films. This phenomenon is more important at smaller target‐collector distances and lower pressures of ambient NH3.

MAPLE deposition and characterization of SnO2 colloidal nanoparticle thin films

In this paper we report on the deposition and characterization of tin oxide (SnO2) nanoparticle thin films. The films were deposited by the matrix-assisted pulsed laser evaporation (MAPLE) technique. SnO2 colloidal nanoparticles with a trioctylphosphine capping layer were diluted in toluene with a concentration of 0.2 wt% and frozen at liquid nitrogen temperature. The frozen target was irradiated with a KrF (248 nm, τ = 20 ns) excimer laser (6000 pulses at 10 Hz). The nanoparticles were deposited on silica (SiO2) and 1 0 0 Si substrates and submitted to morphological (high resolution scanning electron microscopy (SEM)), structural Fourier transform infrared spectroscopy (FTIR) and optical (UV–Vis transmission) characterizations. SEM and FTIR analyses showed that trioctylphosphine was the main component in the as-deposited films. The trioctylphosphine was removed after an annealing in vacuum at 400 °C, thus allowing to get uniform SnO2 nanoparticle films in which the starting nanoparticle dimensions were preserved. The energy gap value, determined by optical characterizations, was 4.2 eV, higher than the bulk SnO2 energy gap (3.6 eV), due to quantum confinement effects.

Multilayer metallization structures with titanium nitride and titanium silicide prepared by multipulse laser irradiation

We synthesized titanium nitride and titanium silicide layers on silicon by only one‐step multipulse laser irradiation of titanium‐coated silicon wafers in a jet of nitrogen, with characteristics appropriate for utilization in metallization schemes with very large scale integration devices.