Abstract
The emission of electrons from the surface of a material into vacuum depends strongly on the material’s work function, temperature, and the intensity of electric field. The combined effects of these give rise to a multitude of related phenomena, including Fowler-Nordheim tunneling and Schottky emission, which, in turn, enable several families of devices, ranging from vacuum tubes, to Schottky diodes, and thermionic energy converters. More recently, nanomembrane-based detectors have found applications in high-resolution mass spectrometry measurements in proteomics. Progress in all the aforementioned applications critically depends on discovering materials with effective low surface work functions. We show that a few atomic layer deposition (ALD) cycles of zinc oxide onto suspended diamond nanomembranes, strongly reduces the threshold voltage for the onset of electron field emission which is captured by resonant tunneling from the ZnO layer. Solving the Schroedinger equation, we obtain an electrical field- and thickness-dependent population of the lowest few subbands in the thin ZnO layer, which results in a minimum in the threshold voltage at a thickness of 1.08 nm being in agreement with the experimentally determined value. We conclude that resonant tunneling enables cost-effective ALD coatings that lower the effective work function and enhance field emission from the device.
Highlights
In contrast to the thermionic (TH) emission captured by the RD equation, electrons can emit from a cold cathode when applying high electric fields[3]
When the electric field at the emitter surface is sufficiently high (~1 × 10 3V. μm−1), field emission even at room temperature is feasible due to lowering of the vacuum potential barrier which eases the escape of electrons from the material into vacuum via tunneling
The doping concentration of which in combination with their rough surface profile according to the crystal growth (Fig. 1(a,b)) turn them into ideal candidates for electron field emission (FE)
Summary
In contrast to the thermionic (TH) emission captured by the RD equation, electrons can emit from a cold cathode when applying high electric fields[3]. At fields up to 108 V.cm−1, the enhanced emission comes from Schottky barrier lowering due to image charges, where the work function is reduced by an applied field F according to ∆Φ = qF/4πε with q and ε being the electron charge and the vacuum permittivity, respectively. It was shown that the work function in large-area monolayer graphene can be lowered by nearly 1 eV through a combination of coating and electrostatic gating[16] Another application field is proteomics: Freestanding nanomembranes employing (phonon-assisted) electron field emission have been utilized as detector units in time-of-flight mass spectrometers for protein analysis. Atomic layer deposition (ALD) based on sequential gas-solid chemical surface reactions allows for a precise thickness tuning in the Ångström range. The deposition of oxides by physical vapor deposition needs a sensitive control of the oxygen content during the deposition process, whereas the composition and stoichiometry of oxides deposited by ALD is defined by the chemical reaction between a metal ion-containing precursor and an oxidant, e.g. water, ozone, or molecular oxygen[22,23]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
