Hexagonal Nanopits with the Zigzag Edge State on Graphite Surfaces Synthesized by Hydrogen-Plasma Etching

Abstract

We studied, by scanning tunneling microscopy, the morphology of nanopits of monolayer depth created at graphite surfaces by hydrogen plasma etching under various conditions such as H2 pressure, temperature, etching time, and RF power of the plasma generation. In addition to the known pressure-induced transition of the nanopit morphology, we found a sharp temperature-induced transition from many small rather round nanopits of ∼150 nm size to few large hexagonal ones of 300-600 nm within a narrow temperature range. The remote and direct plasma modes switching mechanism, which was proposed to explain the pressure-induced transition, is not directly applicable to this newly found transition. Scanning tunneling spectroscopy (STS) measurements of edges of the hexagonal nanopits fabricated at graphite surfaces by this method show clear signatures of the peculiar electronic state localized at the zigzag edge (edge state), i.e., a prominent peak near the Fermi energy accompanied by suppressions on either side in the local density of states. These observations indicate that the hexagonal nanopits consist of a high density of zigzag edges. The STS data also revealed a domain structure of the edge state in which the electronic state varies over a length scale of ∼ 3 nm along the edge. The present study will pave the way for microscopic understanding of the anisotropic etching mechanism and of spin polarization in zigzag nanoribbons which are promising key elements for future graphene nanoelectronics.

Nanoscale Fabrication of Graphene by Hydrogen-Plasma Etching

“…The sudden change of the anisotropic etching at temperature between 400 and 500°C shown in Ref. 18 was reproduced with our setup. By preparing nucleation center for hexagonal nanopit using CHF 3 -plasma, we succeeded to shape a graphene into a desired structure by applying HPE.…”

“…The HPE system was set following the one in Ref. 18, but the diameter of the etching chamber made by quartz tube was smaller (i.d. 30 mm) to make the cooling time shorter.…”

“…Rather recently, it is found that the ideal zigzag edge can be fabricated by etching graphene and graphite surface using H-plasma [15][16][17][18], in which monatomic deep hexagonal nanopits surrounded by zigzag edges are created. The LDOS on the edge shows a sharp peak at E F and the suppression of the LDOS next to the peak suggests that the edge shows zigzag structure with atomic precision [19].…”

Electron transport tuning of graphene by helium ion irradiation

“…In this case, the potential disorder is caused by local sp 3 hybridization, resulting in carrier localization [15]. Another method is the hydrogenation of graphene [22][23][24][25][26], known as graphane. Hydrogenation, in this case, is a reversible process in which conduction can be changed from metallic to insulating.…”

“…Here the potential perturbation is also caused byattributed to local sp 3 hybridization. One interesting work on the hydrogen process in graphene is hydrogenplasma etching, which forms hexagonal nanopits with zigzag-edged straight lines [26]. Instead of using oxygen or hydrogen, the surface modification process was also investigated by chlorination [27,28] or fluorination [29,30].…”