Charge storage in β-FeSi₂ nanoparticles

We report on the observation of a surprisingly high specific capacitance of β-FeSi₂ nanoparticle layers. Lateral, interdigitated capacitor structures were fabricated on thermally grown silicon dioxide and covered with β-FeSi₂ particles by drop or spin casting. The β-FeSi₂-nanoparticles, with crystallite sizes in the range of 10–30 nm, were fabricated by gas phase synthesis in a hot wall reactor. Compared to the bare electrodes, the nanoparticle-coated samples exhibit a 3–4 orders of magnitude increased capacitance. Time-resolved current voltage measurements show that for short times (seconds to minutes), the material is capable of storing up to 1 As/g at voltages of around 1 V. The devices are robust and exhibit long-term stability under ambient conditions. The specific capacitance is highest for a saturated relative humidity, while for a relative humidity below 40% the capacitance is almost indistinguishable from a nanoparticle-free reference sample. The devices work without the need of a fluid phase, the charge storing material is abundant and cost effective, and the sample design is easy to fabricate