Laser-induced structural and composition modification of multilayered Ni/Ti thin film in air and liquids

The interaction of an Er, Yb, Cr-glass laser, operating at 1540 nm wavelength and a pulse duration of 40 ns, with Ni/Ti multilayer thin films has been studied. Five (Ni/Ti) bilayers deposited by DC ion sputtering on Si(100) wafers to a total thickness of about 180 nm were treated with laser fluences of about 6.4 and 8.8 J cm(-2). Single and multi-pulse laser irradiation was done at normal incidence in air, water and ethanol ambients. The composition and surface morphology were monitored by particle-induced x-ray emission, Rutherford backscattering spectrometry (RBS), scanning electron microscopy and profilometry. Most of the absorbed laser energy was rapidly transformed into heat, producing intensive modifications of composition and morphology on the target surface. The results show an increase in surface roughness, formation of parallel periodic surface structures, appearance of hydrodynamic features and ablation of surface material. RBS analysis revealed that laser modification induced inter-mixing between the components of individual Ni and Ti layers, with indications of the formation of NiTi intermetallic compounds. An interesting finding is the morphological changes dominant in the Si substrate, whereas the Ni/Ti multilayer structure has mainly undergone changes in the chemical composition

Detection of Charge Density Wave Ground State in Granular Thin Films of Blue Bronze K0.3MoO3 by femtosecond spectroscopy

During the last years, femtosecond time-resolved spectroscopy (fsTRS) has become an important new tool to investigate low energy excitations in strongly correlated systems. By studying energy relaxation pathways linking various degrees of freedom (e.g., electrons, spin, or lattice), the interaction strengths between different subsystems can be deduced. Here we report on yet another application of fsTRS, where the technique is used to unambiguously determine the nature of the ground state in granular thin films of a prototype charge density wave system blue bronze, K0.3MoO3. These, potassium blue bronze, films, obtained for the first time ever, have been prepared by pulsed laser deposition and investigated by various standard characterization methods. While the results of all used methods indicate that the thin films consist of nanometer grains of K0.3MoO3, it is only the non-destructive fsTRS that demonstrates the charge density wave nature of the ground state. Furthermore, the comparison of the fsTRS data obtained in thin films and in single crystals shows the reduction of the charge density wave transition temperature and of the photoinduced signal strength in granular thin films in respect to single crystals, which is attributed to the granularity and crystal growth morphology