Papers by Keyword: Femtosecond Laser Pulses

Abstract: Anisotropic periodic relief in form of ripples was formed on surface of amorphous hydrogenated silicon (a-Si:H) films by femtosecond laser pulses with the wavelength of 1.25 μm. The orientation of the surface structures relative to laser radiation polarization vector depended on the number of laser pulses N acting on the film surface. When N = 30, the structures with 0.88 μm period were formed orthogonal to the laser radiation polarization; at N = 750 the surface structures had period of 1.12 μm and direction parallel to the polarization. The conductivity of the laser-modified a-Si:H films increased by 3 to 4 orders of magnitude, up to 3.8·10^–5 (Ω∙cm)^–1, due to formation of nanocrystalline Si phase with a volume fraction from 17 to 30%. Anisotropy of the dark conductivity, as well as anisotropy of the photoconductivity spectral dependences was observed in the modified films due to depolarizing influence of periodic microscale relief and uneven distribution of nanocrystalline Si phase within such laser-induced structure.

Abstract: Despite basic optoelectronic properties of metal-organic perovskites are quite robust to defects, thelatter affect performance of related photovoltaic devices made of such promising materials. Recently,direct femtosecond projection lithography appeared as prospective tool for high-performing nondestructivenano- and microstructuring of perovskite films. Here, we study in details how defects affectthe photoluminescence properties of CH3NH3PbI3 hybrid perovskite films patterned with single- andmulti-pulse irradiation with flat-top femtosecond laser pulses. Scanning electron, wide-field multiphoton,photoluminescence and laser confocal microscopies being combined with photoluminescencedecay measurements are carried out for these studies. The obtained experimental results are analyzedwith a model for carriers kinetics allowed to determine contributions from radiative and non-radiative processes.

Abstract: We demonstrated efficient crystallization of amorphous Si films induced by their direct irradiation with near-IR femtosecond laser pulses coming at sub-MHz repetition rate. Comprehensive analysis of morphology and composition of the laser-annealed film by atomic-force microscopy, Fourier-transform IR, Raman and energy dispersive X-ray spectroscopy as well as numerical modeling of optical spectra confirmed efficient crystallization of amorphous Si and high-quality of the obtained films opening pathway for applications in thin-film solar cells, transistors and displays.

Abstract: The influence of the chemical composition of the substrate material on the chemical and phase composition of the formed coating was investigated. A number of experiments aimed at studying the interaction of titanium alloys with ultrashort laser pulses in different reaction media was carried out. A new method for the formation of titanium carbide under the action of ultrashort laser pulses on the surface of a titanium sample in a liquid hydrocarbon and liquid nitrogen medium is described. The description of the experiment is presented. The treated surface was investigated using a scanning electron microscope. Raman spectra from the surface of treated titanium alloys under different exposure conditions are obtained.

Abstract: Experiment on ablation of silicon wafer on different crystallographic facet planes by single laser pulse irradiation was carried out with a femtosecond pulsed laser operating at a wavelength of 780 nm and a pulse width of 160 fs. The quality and morphology of the laser ablated silicon surface were evaluated by atomic force microscopy. The ablation threshold fluences on different crystallographic facet planes were obtained through the relationship between the squared diameter of the craters and pulse energy. The effects of different crystallographic facet planes of silicon wafer on the process of femtosecond laser ablation of silicon wafer were studied.