Practical Electron Microscopy and Database

In both electron- and ion-beam deposition methods, the gaseous precursor molecules containing target elements are introduced near the surface of a substrate. The molecules are adsorbed on the surface, and then are decomposed by an energetic electron- or ion-beam in a vacuum chamber. The volatile products of the precursor are pumped out while the nonvolatile product containing the target elements remains as a deposit. This process is usually performed in scanning electron microscopes (SEMs) and scanning transmission electron microscopes (STEMs) in high spatial accuracy. In practice, the energies of the primary electrons are normally too high (in the range of 10 to 300 keV) to efficiently break the molecular bonds of the precursors. Therefore, the decomposition normally occurs through a two-step process:
         i) The substrate surface near the deposition spot absorbs the primary electrons and emits secondary electrons.
         ii) The emitted secondary electrons decompose the precursor molecules, and then the deposition process occurs.

The EBID may be divided into two categories:
         i) Conventional EBID using conductive substrates. In this case, the conductive substrates provide stable fabrication conditions.
         ii) EBID using insulator substrates. For instance, by using Al₂O₃ and SiO₂ substrates, characteristic morphologies of nanowhiskers (or nanowires), arrays of nanodendrites, and fractal treelike structures have been fabricated in transmission electron microscopes (TEMs) [1,2]. The nanowhisker, the tip of a nanodendrite, and the tip of a nanotree are typically ~3 nm in diameter, and are almost completely independent of the electron beam size.

[1] Song M, Mitsuishi K, Tanaka M, Takeguchi M, Shimojo M and Furuya K 2005 Appl. Phys. A 80 1431.
[2] Xie G, Song M, Mitsuishi K and Furuya K 2005 J. Nanosci. Nanotechnol. 5 615.