Fabrication and STEM/EELS measurements of nanometer-scale silicon tips and filaments

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Abstract
We present a series of scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS) measurements of nanometer-scale single-crystal silicon tips and filaments. The tips and filaments are of a type that we are currently integrating into microelectromechanical systems. The EELS measurements reveal a number of nanometer-scale effects, some of which have already been reported in the literature for other systems. These effects include apparent upward shifts in the energies, widths, and interaction cross sections of the plasmons. In addition, we report a sharp peak at 5 eV, which we are identifying as an interband transition in the silicon. We provide theoretical explanations of the characteristics of this new peak, including an explanation of its failure to appear at any but the smallest sample diameters. Finally, we extend the theory already present in the literature with a finite-element model of EELS for nonpenetrating electrons in an arbitrary geometry.