Structurally Controlled Large-Area 10 nm Pitch Graphene Nanomesh by Focused Helium Ion Beam Milling

Abstract

Graphene nanomesh (GNM) is formed by patterning graphene with nanometer-scale pores separated by narrow necks. GNMs are of interest due to their potential semiconducting characteristics when quantum confinement in the necks leads to an energy gap opening. GNMs also have potential for use in phonon control and water filtration. Furthermore, physical phenomena, such as spin qubit, are predicted at pitches below 10 nm fabricated with precise structural control. Current GNM patterning techniques suffer from either large dimensions or a lack of structural control. This work establishes reliable GNM patterning with a sub-10 nm pitch and an < 4 nm pore diameter by the direct helium ion beam milling of suspended monolayer graphene. Due to the simplicity of the method, no postpatterning processing is required. Electrical transport measurements reveal an effective energy gap opening of up to ∼450 meV. The reported technique combines the highest resolution with structural control and opens a path toward GNM-based, room-temperature semiconducting applications.

Conductance Tunable Suspended Graphene Nanomesh by Helium Ion Beam Milling

“…Some contaminations were found on the suspended GNMs, which prevented the helium ion beam drilling the nanopores. With this kind of large area meshing, the fraction of missing-nanopore rate was relatively low compared with our previous work [32]. In that case, the effect from missing-nanopore to the conductance of GNMs was negligible.…”

“…The nanopore The GNMs were patterned by HIBM on the suspended GNRs in a high vacuum chamber (< 5 × 10 −7 mbar), as shown in Figure 3a. In order to maintain consistent nanopore dimensions and investigate the effect of the nanopores pitch (center to center) for the electrical transport properties of the GNMs, the beam current was kept at 1 pA and the dwell time was kept at 45000 µs based on our previous work [32], where dwell time is how long the beam stays in one nanopore. After patterning, the GNMs were checked directly with the HIB secondary electron microscopy.…”

“…It has a larger driving current and higher on-off ratio than the narrow GNR [26,27]. Most of all, GNM has been reported to observe a transport gap opening both in theoretical simulations [28][29][30] and experiments [31,32]. These results pave the way to use the GNM in electrical logic devices.…”

“…Thus, patterning the large area of GNMs via electron-beam irradiation is impractical. The focused ion beam milling overcomes the limitation of the speed and also provides a reasonable resolution to observe the nanopore array [32].In this work, the suspended GNM devices were fabricated and patterned by focused helium ion beam milling (HIBM) (Figure 1). By optimizing the pattern location, stable suspended GNMs were obtained with different pitches of nanopores, which avoided cracking at edges during the HIBM.…”

“…Thus, patterning the large area of GNMs via electron-beam irradiation is impractical. The focused ion beam milling overcomes the limitation of the speed and also provides a reasonable resolution to observe the nanopore array [32].…”