Experimental study of field emission from ultrasharp silicon, diamond, GaN, and tungsten tips in close proximity to the counter electrode

Abstract

The patterning process in field-emission scanning probe lithography (FE-SPL), a high-resolution and cost-effective method for nanofabrication, is based on the field emission of electrons from ultrasharp tips in close proximity to a sample (distances below 100 nm). Thereby, the emitted electrons expose directly an ultrathin resist film. The field enhancement at the tip apex is crucial for the field emission current, which follows the Fowler–Nordheim theory. Despite the success of FE-SPL in nanofabrication, systematic experimental studies of the field-emission process, including the determination of the tip radius and tip-to-sample distance during the measurement, for these small tip-to-sample distances and different tip materials are lacking. To resolve this issue, experimental measurements of the field-emission current for tip–sample proximity distances below 100 nm were performed. For this purpose, the developed AFM in SEM system was modified,1,2 which enables one to monitor the tip–sample distance with a high accuracy using SEM while simultaneously recording the field-emission current. The authors present experimental results of the dependence of the field-emission current on the tip shape, tip material, applied voltage, and tip–sample distance. Therefore, the emission characteristics of silicon, diamond, GaN, and tungsten tips are shown. The knowledge about the field-emission process for small tip-to-sample distances will help to understand and improve the current FE-SPL, regarding also the choice of tip material. Furthermore, these measurements enable the detailed comparison with current FE models beyond state-of-the-art since all necessary parameters (voltage, current, tip diameter, and tip-to-sample distance) could be measured and controlled during the FE experiment due to the unique experimental system.

Advanced Scanning Probe Nanolithography Using GaN Nanowires

“…Field emission current density as a function of tip–sample distance is also presented in Figure c. As we presented previously, , this plot is typical for the Fowler–Northeim emission. The same GaN tip that was previously used in FE metrology was then used for FE lithography in the ambient condition, and the results are presented in Figures d–g.…”

“…There are a variety of SPL methods that can be classified in terms of the driving mechanism employed in the writing and reading processes, i.e., thermal, , mechanical and diffusive, and electrical. − In electrical or bias-induced SPL, the small size of the tip’s apex and proximity of the conductive substrate can generate considerably high electric fields (∼10 GV m –1 ) by applying relatively moderate voltage (∼10 V) 2 . This confined electric field can be used to modify the chemical/mechanical properties of the molecules on the target substrate.…”

“…Selecting an appropriate tip material plays an important role in determining image and pattern resolution in SPM/SPL . The tip itself must possess three main physical properties; (i) relatively high electrical conductivity, (ii) high mechanical stability (i.e., durability), and (iii) suitable geometry (sharp apex and appropriate cone-angle).…”

Ultralow Voltage GaN Vacuum Nanodiodes in Air

“…This comparison thus shows the enormous benefit of scaling vacuum electronic device gaps down to the nanoscale, allowing for an ∼2 orders of magnitude or greater reduction in turn-on voltage while enabling stable in-air or low-vacuum operation. Our nanogap devices also exhibit record low turn-on and very high currents compared to prior field-emission demonstrations of GaN structures including nanowire arrays and individual nanowires. − We note that the emitter sharpness of our devices is quite modest compared to prior work in the field utilizing emitters with near atomic sharpness, which should greatly improve manufacturability as well as emitter stability and durability.…”

Line edge roughness metrology software

“…The tip-radius of curvature was approximately 15 nm for the presented tip, whereas diameters typically smaller than 10 nm are obtained. 42 The height of the crystallographic Si tip is about 6 μm.…”