ИСТИНА

We report a combined experimental and theoretical investigation on a subnanometric carbon tip with the apex radius of 0.8 nm. The tip was created by field-emission assisted structural modification of a diamond needle-like crystal [1], see figure1. The field emission current-voltage characteristics were measured at a distance of 500 μm between the tip and a flat anode. In particular, a current of less than 1 nA was achieved at a voltage of 80 V. Electrostatic modeling based on TEM images showed that at this voltage the electric field at the emitter apex is about 15 V/nm. When the Fowler- Nordheim (FN) theory was employed to predict the current using the calculated value of the electric field the result was 4*104 nA. On the other hand when the Simmons theory was employed using the calculated full potential variation along the axis the result was 103 nA – a minor improvement on the FN result. Using the generalized FN for nanoscopic emitters [2] did not help either. Satisfactory agreement between theory and experiment that eliminates this difference of orders of magnitude was accomplished when a theory [3] that takes account of the serious distortion of the wavefunctions is employed. This theory is not using simple plane waves for the electron states but takes due account of the emitter shape, see figure2 and takes account also of localization effects. The supply of electrons function of this emitter is radically different from the traditional Fowler-Nordheim one. The implications are discussed.