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Graphite and silicon nanoneedles are fabricated by different etching processes on highly oriented pyrolitic graphite (HOPG) and SiO2/Si. The masks used to engrave such substrates are needle-shaped ...

Formation of a solid solution of Cd1-yMnyS nanocrystals is demonstrated using EXAFS (extended X-ray absorption fine structure).

In this Letter, a model of a Cd1-yMnyS nanocrystal is proposed to explain the appearance of manganese ions isolated in the tetrahedral site, at relatively high composition, whereas magnetic interactions markedly increase in the nanosized range compared to the bulk phase.

In this paper, we present, for the first time, the magnetic properties of Cd1-yMnyS nanocrystals of average size (4 nm) at various compositions, y. We demonstrate that the Mn−Mn interactions are markedly enhanced compared to the bulk material. As in the bulk phase, the photoluminescence and the EPR hyperfine structure, both attributed to isolated Mn2+ ions in a tetrahedral coordination, behave similarly with increasing composition. At the opposite of the bulk phase, isolated Mn2+ ions are observed for a rather large composition (y = 0.08) in nanocrystals. We attempt to relate the change of the band gap with composition with the various manganese interactions.

Absorption and photoluminescence spectroscopic measurements are presented for particles with sizes from 2 to 4 nm, composition from y = 0 to 0.3,where y is given by Cd1-yMnyS, and different preparation modes. No monotonous variation of bandgap energy with increasing composition is observed. The depth of the minimum increases with decreasing particle size. This is attributed to a marked increase in the interactions between the Mn2+ d electrons and the valence and conduction band electrons. Mn2+ photoluminescence is observed at 77 K, when the particles are aged in the solution. Otherwise only the trap emissions due to CdS defect states are seen. Certain preparation modes favor Mn2+ photoluminescence at room temperature.