Electron Emission from Thin Al-Al2O3-Au Structures

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Abstract
Emitter cells with Al2O3 film thicknesses between 67 and 150 Å and Au film thicknesses between 200 and 300 Å were operated at voltages up to 10 V. Typical I‐V characteristics for the total cell currents are presented. The curves suggest tunnel emission through the barrier at the Al‐Al2O3 interface when the cell is operated for the first time and only small currents have been drawn. After passage of large currents, the I‐V characteristics become temperature dependent. The normal energy distribution of the emitted electrons is measured and a linear dependence of the average energy on cell voltages is established. The fractions of current emitted through the Au into the vacuum is determined as a function of the Al2O3 thickness. Using the attenuation lengths of gold reported recently by Mead, an attenuation length of about 24 Å is deduced for electrons, which within the insulator have gained an energy of nearly 3 eV. The emitted current could be increased considerably by depositing a low work function material (Ba) at the gold surface. The maximum fraction of current emitted into the vacuum was 10−2, at an emitted current density of nearly 5 mA/cm2.

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