High-resolution Field-emission Electron Research Articles

Luminescent properties and particle morphology of Ca3(PO4)2:Gd3+, Pr3+ phosphor powder prepared by microwave assisted synthesis

Nanoparticulate Ca3(PO4)2:Gd3+,Pr3+ phosphor powders were synthesized by microwave-assisted methodology in an aqueous medium. The X-ray diffraction patterns of the nanopowders confirmed the successful crystallization of Ca3(PO4)2 that are consistent with the standard rhombohedral phase of Ca3(PO4)2. The average crystallite size calculated using William–Hall equation was 99nm. The high resolution field emission electron microscopy data suggest that the powder consisted of an agglomeration of faceted hexagonal particles. Upon excitation with ultra violet (UV) radiation at 274nm the phosphor exhibited a narrowband emission peak at a wavelength of 313nm corresponding to the 6P7/2→8S7/2 transition of the Gd3+ ion. Upon co-doping with Pr3+ a broad excitation peak at 222nm was observed, which was assigned to the 4f–5d transition of the Pr3+ ion. The peak intensity of the UVB emission at 313nm was shown to improve considerably when excited at 222nm, suggesting that Pr3+ harvested primary excitation energy and transferred it non-radiatively to Gd3+.

High Resolution FESEM and TEM Reveal Bacterial Spore Attachment

Transmission electron microscopy (TEM) studies in the 1960s and early 1970s using conventional thin section and freeze fracture methodologies revealed ultrastructural bacterial spore appendages. However, the limited technology at that time necessitated the time-consuming process of imaging serial sections and reconstructing each structure. Consequently, the distribution and function of these appendages and their possible role in colonization or pathogenesis remained unknown. By combining high resolution field emission electron microscopy with TEM images of identical bacterial spore preparations, we have been able to obtain images of intact and sectioned Bacillus and Clostridial spores to clearly visualize the appearance, distribution, resistance (to trypsin, chloramphenicol, and heat), and participation of these structures to facilitate attachment of the spores to glass, agar, and human cell substrates. Current user-friendly commercial field emission scanning electron microscopes (FESEMs), permit high resolution imaging, with high brightness guns at lower accelerating voltages for beam sensitive intact biological samples, providing surface images at TEM magnifications for making direct comparisons. For the first time, attachment structures used by pathogenic, environmental, and thermophile bacterial spores could be readily visualized on intact spores to reveal how specific appendages and outer spore coats participated in spore attachment, colonization, and invasion.

A New High Resolution Field Emission SEM with Variable Pressure Capabilities

To examine non conductive samples in their natural state (i.e. without significant sample preparation) at high resolution in the SEM the technique of low voltage field emission scanning electron microscopy (LVFESEM) is used. Due to the limitation in accelerating voltage (U<1kV) this technique is limited in respect of chemical analysis. Furthermore it is not possible to examine humid and outgassing samples in high vacuum. in recent years the application of variable pressure scanning electron microscopes (VPSEM) became an important technique in materials science as well as in life science. Due to the capability of maintaining a high chamber pressure humid, outgassing and non-conductive samples, can be examined in their natural state without significant sample modification or preparation. Especially compound materials with different electron yields can be imaged without any charging effects (Fig. 2), [2]. This paper describes a high resolution field emission electron microscope, that combines low voltage and variable pressure capabilities.The high pressure capabilities of the instrument are realized by eliminating the high vacuum requirements of SEM in the microscope chamber. This is done by separating the vacuum environment in the chamber from the ultra high vacuum environment in the gun area.