T. Tunno

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.

Very low roughness MAPLE-deposited films of a light emitting polymer: an alternative to spin coating

The matrix assisted pulsed laser evaporation (MAPLE) technique is emerging as an alternative route to conventional deposition methods of organic materials (solution-phase and thermal evaporation approaches). However, the high surface roughness of the films deposited by MAPLE makes this technique not compatible with applications in electronics and photonics. In this paper we report the deposition of MAPLE-films of a green light emitting polymer, commercially named ADS125GE, with remarkable low roughness values, down to about 10 nm at the thickness conventionally used in photonic devices (~40 nm). This issue is discussed as a function of polymer concentration, target-substrate distance and substrate rotation based on AFM topography images, roughness estimation and optical (absorption and luminescent) measurements. In addition we have fabricated an organic light emitting diode with this technique using the best deposition parameters which guarantee the lowest roughness. These results open the way to MAPLE applications in organic photonics and opto-electronics.

Pulsed laser deposition of Pr3+- doped chalcogenide thin films for optical applications

Thin films of Praseodymium-doped chalcogenide glasses [GeS2-Ga2S3-CsI] were prepared by pulsed laser deposition (PLD) technique. The targets were ablated using XeCl (308 nm) and KrF (248 nm) excimer lasers. The films were deposited on microscope glass slides, SiO2 plates and lithium niobate (LiNbO3) substrates at room temperature and at 300 °C. Morphological, compositional and structural characteristics of deposited films were investigated by different techniques. (Rutherford backscattering spectrometry, scanning electron microscopy and x-ray diffraction). Optical transmission of films and target, at normal incidence, were recorded in the 200-3500 nm spectral region. The optical constants (refractive index n and extinction coefficient k) vs wavelength, as well as the film thickness, were calculated from these spectra with the aid of a computer code. The presence of praseodymium in the doped chalcogenide thin film was analysed by exciting the electrons to the 1G4 level and collecting the photoluminescence spectrum in the 1.335 µm region. The waveguiding properties of the deposited films were investigated by the prism coupling technique (m-lines spectroscopy).

Nanoparticle thin films deposited by MAPLE for sensor applications

We report on the potentiality of the Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique for the deposition of thin films of colloidal nanoparticles to be used for gas sensors based on electrical transduction mechanisms. The MAPLE technique seems very promising, since it permits a good thickness control even on rough substrates, generally used to enhance the active surface for gas adsorption. TiO2 (with a capping layer of benzyl alcohol) and SnO2 (with a capping layer of trioctylphosphine) colloidal nanoparticles were diluted in suitable solvents (0.2% concentration), frozen at liquid nitrogen temperature and ablated with a ArF (λ=193 nm) or KrF (248 nm) excimer laser. The nanoparticle thin films were deposited on silica, interdigitated alumina and <100> Si substrates and submitted to morphological (SEM-FEG), structural (XRD, FTIR), optical (UV-Vis transmission) and electrical (sensing tests) characterizations. A uniform distribution of TiO2 nanoparticles, with an average size of ~10 nm, was obtained on flat and rough substrates. The deposited TiO2 nanoparticles preserved the anatase crystalline structure, as evidenced by the XRD spectra. FTIR analysis showed that the SnO2 nanoparticles maintained the capping layer after the laser-assisted transfer process. This protective layer was removed after annealing at 400 °C. The starting nanoparticle dimensions were preserved also in this case. Electrical tests, performed on TiO2 nanoparticle films, in controlled atmosphere in presence of ethanol and acetone vapors, evidenced a high value of the sensor response even at very low concentrations (20-200 ppm in dry air). In contrast, in the case of SnO2 nanoparticle films, electrical tests to ethanol vapor presence showed poor gas sensing properties probably due to the small nanoparticle sizes and interconnections.