Formation of core-shell and hollow nanospheres through the nanoscale melt-solidification effect in the Sm-Fe(Ta)-N system.

Sm-Fe-Ta-N-O nanospheres were synthesized by pulsed-laser deposition from a Sm(13.8)Fe(82.2)Ta(4.0) target in a nitrogen atmosphere. Three structurally and compositionally distinct types were identified: amorphous, core-shell and hollow nanospheres. Amorphous spheres were compositionally homogeneous and completely oxidized. The core-shell spheres were composed of an iron-rich crystalline core with up to 10 at.% interstitially incorporated nitrogen, surrounded by an amorphous and oxidized shell. The hollow spheres were characterized by voids filled with N(2) gas. It was found that the formation of either amorphous or complex nanospheres is defined by an initial Fe/Sm ratio within the molten droplet. The formation of hollow spheres is believed to be related to the general affinity of liquid metals for gas intake. During rapid solidification the dissolved gas in the melt is trapped within the surrounding solid rim, preventing the outwards diffusion of gas. As long as the amount of gas atoms in the melt is kept below its solubility limits it can be completely interstitially incorporated into the solid, thus forming crystalline Fe(N)-rich cores. If the melt contains more than an equilibrium amount of nitrogen it is possible that the gas recombines to form N(2) molecules, which are condensed inside the spheres.

Photodissociation dynamics of DNA bases.

In order to access the damaging mechanismsof DNA and its bases on themolecular level by T Hz radiation, it isnecessary to create a database of assessingdamage at different spectral regions.Possible damage by T Hz radiation will beassessed by comparison. Furthermore, theexpose of the cytosine to radiation at157 nm, suggest that photochemical bondbreaking is the only damaging mechanism inthe vacuum ultraviolet region of thespectrum, (157-170) nm where one photonbreaks one chemical bond.

VUV and UV fluorescence and absorption studies of Pr(3+)-doped LiLuF(4) single crystals.

The laser-induced fluorescence spectrum of LiLuF(4):Pr(3+) single crystals, pumped by an F(2) pulsed-discharge molecular laser at 157 nm, was obtained in the VUV and UV regions of the spectrum at room temperature. A number of new fluorescence peaks were observed for the first time to our knowledge. They were assigned to the dipole-allowed transitions 4f5d ? 4f(2) of Pr(3+) ion. In addition, the absorption spectrum of the crystal samples was recorded. The positions of the bands with the 4f5d configuration were found to be 46 412, 53 267, and 63 397 cm(-1) from the ground state, (3)H(4), of the Pr(3+) ion. The edge (onset) of the 4f5d bands was at 45 100 cm(-1).