The following text is an extract from a paper published by the National Nano Devices Laboratories (NDL), Taiwan:

Comparison of field emission properties between single silicon emitter and silicon emitters array are investigated in this letter by utilizing a scanning electron microscopy (SEM) with a small tungsten probe having apex radius approximately 90nm. The inter-electrode distance is controlled within tens of nanometers. Measured I-V data fitted using Fowler-Nordheim model revealed that the turn-on field of an individual emitter is much higher than that of emitter array consisting of 288 nearly identical emitters. This observation is further supported by the simplified electric-field calculation. Experimental results also indicate that the anode area may be an important factor of in determining field emission.

SEM image of Si nanotips array with height of 20 µm.

Field emission is measured by aligning the emitter and the anode apex în a small separation by SEM:

Alignment procedure: the top tip is the Tungsten anode, the lower tip is one of the Si emitters.

The voltage to tip distance relationship is described in the next two diagrams:

Field emission behavior of (a) a single emitter with a tip gap distance of 46 nm and (b) a tip gap distance of 50 µm .

Conclusion:

Field-emission properties have been studied intensively with various materials in the past decade, in which performance was found to strongly depend on the inherence, morphology and the density of materials, to name a few. Possible commercial aplications have been demonstrated, but the performance varies strongly with the electrode properties. Therefore, electron emission based on silicon materials is of great importance due to the advantage in integrating silicon-based vacuum microelectronics and silicon integrated circuit technology.