ИСТИНА

An observation of a Coulomb staircase in the current-voltage characteristic of field emission (FE) from a single crystal diamond needle at room temperature is reported. The diamond needles were produced by selective oxidation of polycrystalline CVD diamond films. The needles had shape close to a square-based pyramid with a height of ~50 µm, a thickness at the base of ~1 µm and a tip apex radius of ~50 nm. FE was observed from the apex of a needle using an UHV system equipped with an electron spectrometer. At FE currents below 100 nA the needles demonstrated a strong saturation in the Fowler-Nordheim (FN) plots usually observed for highly resistive emitters. At higher current the needles underwent abrupt decrease of the resistance and consequently their FN plots became much less saturated. After this transformation the FE current increased in a step-like fashion during the voltage ramp. Such staircase behavior was previously predicted theoretically for nanoscale field emitters and explained by the Coulomb blockade effect. Transmission electron microscopy (TEM), Raman spectroscopy and electron energy loss spectroscopy (EELS) were used to characterize structural changes after the FE experiment. It was found that the diamond needle is covered by a layer of amorphous carbon which is responsible for the resistance decrease. Furthermore, the TEM revealed a nanoscale protrusion on the apex of the needle which can explain Coulomb blockade behavior. The analysis of the obtained data and discussion of the results will be presented.