High-resolution investigations of ripple structures formed by femtosecond laser irradiation of silicon.

We report on the structural investigation of self-organized periodic microstructures (ripples) generated in Si(100) targets after multishot irradiation by approximately 100-fs to 800-nm laser pulses at intensities near the single shot ablation threshold. Inspection by surface sensitive microscopy, e.g., atomic force microscopy (AFM) or scanning electron microscopy (SEM), and conventional and high-resolution transmission electron microscopy reveal complex structural modifications upon interaction with the laser: even well outside the ablated area, the target surface exhibits fine ripple-like undulations, consisting of alternating crystalline and amorphous silicon. Inside the heavily modified area, amorphous silicon is found only in the valleys but not on the crests which, instead, consist of highly distorted crystalline phases, rich in defects.

Raman microscopic investigations of BaTiO(3) precursors with core-shell structure.

Due to their outstanding dielectric and ferroelectric properties, barium titanate (BaTiO(3))-based ceramics have found many applications in electronic devices. To optimise the final quality of such ceramics, a detailed knowledge of the complex processes involved in the formation of BaTiO(3) is required. The phase formation process in ordered structures of the BaCO(3)/TiO(2) system was analysed by X-ray diffraction and by Raman spectral imaging (RSI) as a function of the annealing temperature. RSI was used for the first time as a locally resolving method for phase analysis, and proved to be a useful tool in examining the formation process of BaTiO(3) starting from spherical, core-shell structured precursors of the type TiO(2) core/BaCO(3) shell. The Raman spectra of different BaO-TiO(2) phases appearing as intermediate phases during the formation of BaTiO(3) were recorded for separately-prepared pure substances. Using these spectra as fingerprints, and choosing phase filters by setting wave number windows, "phase landscape pictures" of the samples at different temperatures during the genesis of BaTiO(3) could be created with a lateral resolution of up to 200 nm. These pictures confirm shell-like formation of the different barium titanate phases according to the diffusion of barium and oxygen ions from the Ba-rich shell into the TiO(2) core. At an intermediate state of the phase formation process, the phase sequence Ba(2)TiO(4), BaTiO(3), BaTi(2)O(5), BaTi(4)O(9) and BaTi(5)O(11) to TiO(2) was detected from the outer to the inner parts of the core-shell structures.