Thermionic Emission Energy Distributions From Nanocrystalline Diamond

Thermionic electron emission provides a means of direct energy conversion. Some of the benefits of thermionic power generation include: compactness, scalability, stability, lack of moving parts, and applicability to microscale devices. Taking advantage of these benefits requires the analysis and subsequent manufacturing of materials that emit electrons efficiently and at reasonable temperatures (<1000 °C). We report here on a study being performed to characterize the emission properties of such materials, namely, nanocrystalline diamond with hydrogen and oxygen termination. A hemispherical energy analyzer is used to measure the electron energy distribution from this nanostructured material at elevated temperatures. The effective work function and the presence of regions of differing work functions are determined. Measurements of thermionic emission energy distributions (TEEDs) at temperatures ranging from 573 to 778 °C are presented. The TEEDs show an intriguing development of multiple peaks at higher temperatures, possibly indicating instability in the emitter’s surface chemistry.

Magnetic microstructure imaging by secondary electron spin polarization analysis

Recent research has shown that the low energy secondary electrons generated from ferromagnetic material are spin polarized. The secondary electron polarization yields a signal which is directly proportional to the magnitude and direction of the magnetization within the volume of material in which the electrons were generated. This signal can be used in a scanning electron microscope to image the microstructure of magnetic domains on the surface of ferromagnetic materials.We have incorporated a new compact spin polarization analyzer into a commercial UHV SEM. A schematic diagram of the apparatus is shown in Fig. 1. The secondary electrons are extracted from the sample and are then focused into a hemispherical energy analyzer which filters out the high energy electrons.