A fluorescence-amplifying method based on photonic crystal (PC) has been demonstrated for trace TNT detection. The fluorescence enhancement for TNT detection on the optimized PC can be up to 60.6-fold in comparison to that of the control sample, which combines the slow photon effect of PC and large surface areas of the inverse opal structure. Furthermore, the quenching efficiency of the PC-based sensor achieves 80% after exposure to TNT vapor for 300s. The results suggest that the fluorescenceamplifying method based on PC has enormous potential for the development of highly efficient fluorescence sensors toward detection of trace TNT or other explosives.

The structural stability of FePt nanoparticles of about 5-6nm diameter was investigated by dynamic high resolution transmission electron microscopy. The FePt icosahedra were very stable under an electron beam flux of～20 A/cm2 at 300 kV. Surface sputtering was suppressed due to the large sputtering threshold energy of a Pt-rich shell. Under a flux of～50 A/cm2, the trapping potential well of the FePt particle on the supporting carbon film was lowered by the magnetic interaction between the electron beam and the particle, which leads to rotational and translational motions of the particle. A large dose of electrons (of～200 A/cm2) initiated melting and recrystallization of the FePt particle. The structure of the FePt nanoparticle, a Pt enriched shell around an Fe/Pt magnetic core, is believed to be responsible for its dynamic behaviour under different beam conditions.

Surprisingly oxidation resistant icosahedral FePt nanoparticles showing hard-magnetic properties have beenfabricated by an inert-gas condensation method with in-flight annealing. High-resolution transmission electronmicroscopy (HRTEM) images with sub-Angstrom resolution of the nanoparticle have been obtained withfocal series reconstruction, revealing noncrystalline nature of the nanoparticle. Digital dark-field methodcombined with structure reconstruction as well as HRTEM simulations reveal that these nanoparticles haveicosahedral structure with shell periodicity. Localized lattice relaxations have been studied by extracting theposition of individual atomic columns with a precision of about (0.002 nm. The lattice spacings of (111)planes from the surface region to the center of the icosahedra are found to decrease exponentially with shellnumbers. Computational studies and energy-filtered transmission electron microscopy analyses suggest thata Pt-enriched surface layer is energetically favored and that site-specific vacancies are formed at the edges offacettes, which was experimentally observed. The presence of the Pt-enriched shell around an Fe/Pt coreexplains the environmental stability of the magnetic icosahedra and strongly reduces the exchange couplingbetween neighboring particles, thereby possibly providing the highest packing density for future magneticstorage media based on FePt nanoparticles.