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A fine Au powder, with a mean particle diameter of 4 nm, has been successfully fabricated. The crystalline structure of the 4 nm Au nanoparticles remains in fcc symmetry. No structural changes were found between 15 and 450 K. A crossover from a positive thermal expansion at low temperatures to a negative thermal expansion at high temperatures was observed in the fcc cell parameter at about 125 K. Anomalies associated with the crossover were also observed in the magnetic response and the heat capacity measurements. The observations can be reasonably well interpreted by accounting for the effects of the valence electron potential on the equilibrium lattice separations, with a weakly temperature dependent level spacing.

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The crystal structure and magnetic ordering of the Mn spins in polycrystalline NdMnO3 have been investigated by means of neutron diffraction and ac magnetic susceptibility measurements. The compound crystallizes into an orthorhombic symmetry of space group Pbnm. Three peaks were observed in the temperature dependence of the in-phase component of the ac susceptibility, χ′(T). Neutron diffraction measurements show that all three peaks observed in χ′(T) are of magnetic origin, and are associated with the ordering and the reorientation of the Mn spins. Both ferromagnetic and antiferromagnetic couplings between the Mn spins were observed, resulting in a noncollinear magnetic structure. The Mn spins order at Tm≈75 K, and the moment saturates at ∼20 K at 〈μz〉=2.21 μB.

A new resolution-enhanced surface plasmon resonance (SPR) biosensor offers a tenfold improvement in resolution compared with conventional SPR biosensors in the detection of the surface coverage of biomaterials. The proposed optical biosensor, based on the attenuated total-reflection method, excites both the surface plasmons and particle plasmons to enhance the local electromagnetic field by control of the size and volume fraction of embedded Au nanoparticles to increase the resolution of the device. The SPR biosensor design is based on the Maxwell-Garnett model and the Fresnel equations, and the device is fabricated with a cosputtering deposition system.