RESUMO
The modulation transfer function, noise transfer function and detection quantum efficiency of both 1k2 and 2k2 cameras attached to the same 300 kV FEGTEM have been measured. The results show that both the MTF and the DQE of the 2k2 camera are lower than for the 1k2 camera at frequencies above a third of the Nyquist limit. This lower per-pixel performance of the 2k2 camera is primarily a result of the use of a thicker phosphor scintillator. However, MTF and DQE of the 2k2 camera operated as an effective 1k2 camera by using 2 x 2 pixel binning are superior to the 1k2 camera in the medium spatial frequency range.
RESUMO
The complete crystallography of a one-dimensional crystal of potassium iodide encapsulated within a 1.6-nanometer-diameter single-walled carbon nanotube has been determined with high-resolution transmission electron microscopy. Individual atoms of potassium and iodine within the crystal were identified from a phase image that was reconstructed with a modified focal series restoration approach. The lattice spacings within the crystal are substantially different from those in bulk potassium iodide. This is attributed to the reduced coordination of the surface atoms of the crystal and the close proximity of the van der Waals surface of the confining nanotube.
RESUMO
Eu2O3 nanocrystals are synthesized by a colloidal precipitation route in the size range 2-40 nm. The nanocrystals are passivated with a surface layer of trioctyl phosphine oxide (TOPO) in order to eliminate surface recombination effects. When pumped at 254 nm (4f --> 5d transition) the nanocrystals exhibit red luminescence characteristic of 5D0 --> 7Fn Eu3+ transitions within the cubic form of Eu2O3. The efficiency of the luminescence is increased by a factor of five as the particle size drops below 10 nm; it is suggested that confinement of the long lifetime Eu3+ excitation within the nanocrystal is responsible for this effect. Copyright 1999 Academic Press.