Design of an Einzel Lens with Square Cross-Section

In this paper, the results of modeling and simulation of a microcolumn are presented. The microcolumn is part of a developed miniature MEMS electron microscope equipped with a miniature MEMS high-vacuum micropump. Such an arrangement makes this device the first stand-alone miniature electron-optical device to operate without an external high-vacuum chamber. Before such a device can be fabricated, research on particular elements must be carried out to determine the working principles of the device. The results of the calculations described in this article help us to understand the work of a microcolumn with square holes in the electrodes. The formation of an electron beam spot at the anode is discussed. Further calculations and results show the dependence of the Einzel lens size on the electron beam spot diameter, electron beam current, and microcolumn focusing voltage. The results are used to define the optimal design of the developed MEMS electron microscope.

Influence of ice structure on the soft UV photochemistry of PAHs embedded in solid water

Context. The UV photoreactivity of polycyclic aromatic hydrocarbons (PAHs) in porous amorphous solid water has long been known to form both oxygenated photoproducts and photofragments. Aims. The aim of this study is to examine the influence of ice structure on reactivity under soft UV irradiation conditions. Methods. Mixtures of PAHs with amorphous solid water (porous and compact) and crystalline (cubic and hexagonal) ices were prepared in a high vacuum chamber and irradiated using a mercury lamp for up to 2.5 h. Results. The results show that the production of oxygenated PAHs is efficient only in amorphous water ice, while fragmentation can occur in both amorphous and crystalline ices. We conclude that the reactivity is driven by PAH–water interactions in favourable geometries, notably where dangling bonds are available at the surface of pores. Conclusions. These results suggest that the formation of oxygenated PAH molecules is most likely to occur in interstellar environments with porous (or compact) amorphous solid water and that this reactivity could considerably influence the inventory of aromatics in meteorites.

Memory Effect in Simple Cu Nanogap Junction

We have investigated the resistance switching effect in Cu nanogap junction. Nanogap structures were created by means of electromigration and their electrical properties were measured in a high vacuum chamber. The measured current-voltage characteristics exhibited a clear negative resistance and memory effect with a large on-off ratio of over 105. The estimation from I-V curves indicates that the resistance switching was caused by the gap size change, which implies that the nanogap switching (NGS) effect also occurs in Cu electrodes, a popular wiring material in an integrated circuit.