title: Nanostructuring of GeTiO amorphous films by pulsed laser irradiation.
abstract: Laser pulse processing of surfaces and thin films is a useful tool for amorphous thin films crystallization, surface nanostructuring, phase transformation and modification of physical properties of thin films. Here we show the effects of nanostructuring produced at the surface and under the surface of amorphous GeTiO films through laser pulses using fluences of 10-30 mJ/cm(2). The GeTiO films were obtained by RF magnetron sputtering with 50:50 initial atomic ratio of Ge:TiO2. Laser irradiation was performed by using the fourth harmonic (266 nm) of a Nd:YAG laser. The laser-induced nanostructuring results in two effects, the first one is the appearance of a wave-like topography at the film surface, with a periodicity of 200 nm and the second one is the structure modification of a layer under the film surface, at a depth that is related to the absorption length of the laser radiation. The periodicity of the wave-like relief is smaller than the laser wavelength. In the modified layer, the Ge atoms are segregated in spherical amorphous nanoparticles as a result of the fast diffusion of Ge atoms in the amorphous GeTiO matrix. The temperature estimation of the film surface during the laser pulses shows a maximum of about 500 °C, which is much lower than the melting temperature of the GeTiO matrix. GeO gas is formed at laser fluences higher than 20 mJ/cm(2) and produces nanovoids in the laser-modified layer at the film surface. A glass transition at low temperatures could happen in the amorphous GeTiO film, which explains the formation of the wave-like topography. The very high Ge diffusivity during the laser pulse action, which is characteristic for liquids, cannot be reached in a viscous matrix. Our experiments show that the diffusivity of atomic and molecular species such as Ge and GeO is very much enhanced in the presence of the laser pulse field. Consequently, the fast diffusion drives the formation of amorphous Ge nanoparticles through the segregation of Ge atoms in the GeTiO matrix. The nanostructuring effects induced by the laser irradiation can be used in functionalizing the surface of the films.
authors.affiliation: National Institute of Materials Physics, 105 bis Atomistilor Street, 077125 Bucharest-Magurele, Romania.
authors.forename: Valentin Serban
authors.initials: VS
authors.lastname: Teodorescu
authors.affiliation: National Institute of Materials Physics, 105 bis Atomistilor Street, 077125 Bucharest-Magurele, Romania.
authors.forename: Cornel
authors.initials: C
authors.lastname: Ghica
authors.affiliation: National Institute of Materials Physics, 105 bis Atomistilor Street, 077125 Bucharest-Magurele, Romania.
authors.forename: Adrian Valentin
authors.initials: AV
authors.lastname: Maraloiu
authors.affiliation: National Institute of Materials Physics, 105 bis Atomistilor Street, 077125 Bucharest-Magurele, Romania.
authors.forename: Mihai
authors.initials: M
authors.lastname: Vlaicu
authors.affiliation: National Institute of Materials Physics, 105 bis Atomistilor Street, 077125 Bucharest-Magurele, Romania.
authors.forename: Andrei
authors.initials: A
authors.lastname: Kuncser
authors.affiliation: National Institute of Materials Physics, 105 bis Atomistilor Street, 077125 Bucharest-Magurele, Romania ; Academy of Romanian Scientists, Bucuresti 050094, Romania.
authors.forename: Magdalena Lidia
authors.initials: ML
authors.lastname: Ciurea
authors.affiliation: National Institute of Materials Physics, 105 bis Atomistilor Street, 077125 Bucharest-Magurele, Romania.
authors.forename: Ionel
authors.initials: I
authors.lastname: Stavarache
authors.affiliation: National Institute of Materials Physics, 105 bis Atomistilor Street, 077125 Bucharest-Magurele, Romania.
authors.forename: Ana M
authors.initials: AM
authors.lastname: Lepadatu
authors.affiliation: National Institute of Plasma Lasers and Radiation, 409 Atomistilor Street, 077125 Bucharest-Magurele, Romania.
authors.forename: Nicu Doinel
authors.initials: ND
authors.lastname: Scarisoreanu
authors.affiliation: National Institute of Plasma Lasers and Radiation, 409 Atomistilor Street, 077125 Bucharest-Magurele, Romania.
authors.forename: Andreea
authors.initials: A
authors.lastname: Andrei
authors.affiliation: National Institute of Plasma Lasers and Radiation, 409 Atomistilor Street, 077125 Bucharest-Magurele, Romania.
authors.forename: Valentin
authors.initials: V
authors.lastname: Ion
authors.affiliation: National Institute of Plasma Lasers and Radiation, 409 Atomistilor Street, 077125 Bucharest-Magurele, Romania.
authors.forename: Maria
authors.initials: M
authors.lastname: Dinescu
keywords: GeTiO film; cross-sectional transmission electron microscopy (XTEM); fast diffusion; nanostructuring; pulsed laser annealing