Nanoscale vacuum devices have previously been fabricated using a granular AuPd self-aligned mask to produce both diode and triode structures [1]. The cathode structure consisted of an array of tungsten field emitter pillars, each capped with a AuPd grain, of diameter 1nm and height 10nm approximately. These devices exhibited very low turn-on voltages (typically less than 10V) and could be operated in air or vacuum as the mean free path of electrons of this energy was less than the anode-cathode separation.In these devices the field-emitted current is dominated by emission from a single most-favoured pillar, which could easily be destroyed by excessive current. This resulted in steps in the emission current as successor pillars (next most-favoured) took over and non-traceability in I-V sweeps. In triode devices, but not diode devices, operated at currents below the threshold for damage, repeatable fluctuations in transconductance were observed. These fluctuations were attributed to electron wave interference effects in the collimated beam of the triode between the anode and cathode [2]. The observation of these quantum effects implied a very high degree of source coherence from the nanoscale field emitter. In this study the effect of introducing a semiconductor based barrier, between the AuPd grain and the cathode terminal connection, is studied.
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